Battery Testing a mobility scooter -interpreting readings.

[dishman]

Just testing a battery on a mobility scooter that has two 12v batteries.

Wanting some help interpreting.
From youtube videos, they suggest using a multimeter in the charging port when the scooter is on. It indicates a fully charged two 12V battery scooter should put out around 24V, but often 25V or even 26V.

They then suggest the main test is to check the voltage under load. The guidance being that the voltage should not drop too much. Usually no lower than 23V and certainly no lower than 22V.

The scooter I was testing was not recently fully topped up on charge, so it made interpreting what I saw a bit of a challenge. With the multimeter in the port, and the scooter powered off, I got a reading just over 24V.

As soon as I powered up the scooter this dropped to around 19V or just below. Under load, on the scooter's slowest mode on a flat-ish ground, this dropped to the low 18V. Turned up to full speed and a very slight incline, this dropped to around the mid 17V.
Now, is the issue that the scooter may not have been fully charged? So my baseline for judging the voltage should have been focused on the difference between the static (stationary) Voltage of 19V and the reading when under load of 18V.

Or, is the fact that it was anything below 20V regardless of how recently topped up it was, a strong indication that the battery is certainly well past it's best.

 

[flameport]

2x fully charged lead acid batteries should be around 26 or 27 volts.

Yours were either not charged, or more likely ruined.
Lead acid batteries in that application do not last particularly long, typically a few 100 cycles at most.

 

[blup]

The resistance of any battery will increase as the voltage drops, so make sure it is fully charged. If it is a new battery it might need 4 or 5 cycles. Machine mart do fairly cheap battery condition testers.

Blup

 

[Rodders53]

Mobility scooter batteries are two in series so nominal 24V. Usually lead acid (VRLA, AGM, Gel) but some are now using Lithium (if Lithium ignore the next passages).

Fully charged no load (after any surface charge from recharging has been removed) @ 10 Celsius = 25.542 Volts (100%), 25.142 V (75%) and 24.542 (50% charge). Volts only measured under no load. After load is removed the volts will recover somewhat.

Put them on charge using a smart scooter charger (most are) and wait until it's green. Then repeat some readings. NB Smart charger could well get to > 28.2V during the process as that's what absorbed glass mat lead acids need during the multi-stage charging process.

The big test for mobility scooter batteries is how far and fast will they go... and how that compares to when the batteries were brand new. Exhausted batteries slow down and stop on inclines. Most scooters have some form of voltage/state readout --- coloured leds or an regular analogue needle meter showing good (green) and warning (red).

I'd not expect any significant volt drop when electronics are just switched on (unless the scooter has lots of filament lamps ON). Under movement, yes.

I have some experience of such batteries and chargers; but only in a diy capacity.

NB Try to never discharge below 50%.

 

[dishman]

2x fully charged lead acid batteries should be around 26 or 27 volts.

Yours were either not charged, or more likely ruined.
Lead acid batteries in that application do not last particularly long, typically a few 100 cycles at most.

Ahh, so the results could have been skewed by lack of recent charging?
I was not sure how the voltage reading might be affected a battery that was...perhaps...80% charged. It was likely a few weeks had gone by since it was last fully charged. The scooter's own dial meter (probably a crude guide) was indicating it was maybe 1/6th down.

But you would lean more towards them likely being dud?

How is voltage normally affected by battery drain on a good battery vs a poor one as the scooter is used.

On a new battery does voltage stay at a consistent level for longer before it is drained? Whereas a bad battery the voltage starts to decline immediately?

Is it possible to diagnose a partially charged battery being good or bad with just a multimeter?

Appreciate the help as always!

 

[dishman]

Mobility scooter batteries are two in series so nominal 24V. Usually lead acid (VRLA, AGM, Gel) but some are now using Lithium (if Lithium ignore the next passages).

Fully charged no load (after any surface charge from recharging has been removed) @ 10 Celsius = 25.542 Volts (100%), 25.142 V (75%) and 24.542 (50% charge). Volts only measured under no load. After load is removed the volts will recover somewhat.

Put them on charge using a smart scooter charger (most are) and wait until it's green. Then repeat some readings. NB Smart charger could well get to > 28.2V during the process as that's what absorbed glass mat lead acids need during the multi-stage charging process.

The big test for mobility scooter batteries is how far and fast will they go... and how that compares to when the batteries were brand new. Exhausted batteries slow down and stop on inclines. Most scooters have some form of voltage/state readout --- coloured leds or an regular analogue needle meter showing good (green) and warning (red).

I'd not expect any significant volt drop when electronics are just switched on (unless the scooter has lots of filament lamps ON). Under movement, yes.

I have some experience of such batteries and chargers; but only in a diy capacity.

NB Try to never discharge below 50%.

Thank you. I only saw this after my reply above.

So....based on that information. It would indicate the batteries in this scooter were toast?
Some extra context, this was a potential purchase, so I only had limited opportunity (and a multimeter) to test if it was worth it or not.

 

[ericmark]

Assuming lead acid absorbed glass mat.

As said, first the batteries need to be fully charged, this is the biggest hurdle. It takes time, most chargers will pulse charge, they take it to 14.4 volt on a 12 volt battery, then allow it to drop to 12.8 volt, and repeat, it can take a few weeks, and because a shorted cell with 24 volt will destroy the good battery as well, better doing it at 12 volt.

 

[flameport]

Some extra context, this was a potential purchase

If it's a scooter that's been used moderately often and it's more than a couple of years old, pretty much guaranteed the batteries will need to be replaced.

 

[dishman]

Indeed. This did suggest it had been recently serviced and the vague potential the batteries might have been replaced 6 months ago. But, without firm confirmation, and the multimeter readings I got, I backed out. Still, something to learn regarding what to look out for regarding voltages.

 

[blup]

If in doubt the price you offer should factor in the cost of new batteries.

Blup

 

[Rodders53]

We bought a Pride Celebrity scooter from an acquaintance of ours whose husband had died. It had been unused for months and the batteries "well dead". It has 2x 40Ah batteries in it. This larger scooter with pneumatic tyres and some suspension, was to supplement a smaller shopping scooter with solid wheels that lives in the car with a hoist to get it in/out.

Charged up using the Maker's supplied smart charger in the sellers home for something like 24 hours (14 V+, 13.8 V bulk and 12.7/8 float at different currents). Took a punt and drove it home (I was prepared to push it back if needed and then buy new batteries). {We'd tried a shorter charge on the day over a cup of tea with no success.}

Those batteries are still in the scooter and work well enough for our use (a few miles around the village / parks occasionally). That's some 8 years later. That one has an analogue meter with red, yellow and green bands. Pride say to check the meter at full speed on level ground -- red means recharge asap... yellow 'draining', green OK.https://www.tayna.co.uk/mobility-batteries/powerline/pl45-12-pair/

A pair of cheaper brand batteries for that scooter today would be around £120 today

Pair of 12V 40Ah Mobility Batteries - Powerline PL45-12

A pair of Powerline Sealed Lead Acid Batteries.

www.tayna.co.uk

I factor in 3-yearly replacements for the shopping scooter (18-22 Ah batteries) and have two battery packs packs on the go at the moment. Both sets are over 3 years old (one is 4 in May) and have been recharged 112/113 times. Lucas and Yuasa branded £85 and £90 the pairs respectively. We can tell they are nearing end of life when the range starts noticeably reducing.
I don't recharge the batteries after every use (as the backup pack is available) and it's not needed if only used around a supermarket, say.

NB. The first scooter we bought new had a faulty charger which fried two sets of batteries... by the third I'd learned to disconnect the charger as soon as it went 'green' onto float charge (at wrong voltage or current, I never quite knew). That one was replaced when bits started going wrong with it, with another and a different functional charger (which is how we have two battery packs).

 

[ericmark]

My mothers old scooter had 2 x 40 Ah AGM batteries, one cell went short circuit after 15 years of use, and fried the other battery of the pair, replaced with Tayna (Manchester Batteries) and it gets a charge every couple of months, but scooter not really used, my wife and I prefer the e-bikes.

So time it is sold or got rid of, however may use the batteries, would run emergency lights a treat.

However as to batteries, on the death of my father-in-law we found a collection of batteries, from all sorts from stair lift to caravan, most completely discharged, I was always of the opinion once left fully discharged really ready for the bin, but thought where the harm, lets give it a go.

Hurdle one is the Lidi smart charger will not charge a fully discharge battery, and two if there is a shorted cell one would not know until other cells start to work, so one can easy end up with a fried battery.

So batteries were put in parallel with a good battery to get charger to work, and charger connected to energy monitor which was on Firefox start up page so I could see if all OK every time I started up Firefox.

The result was not what I as an Auto Electrician had expected, the donor battery would quickly charge, and the charger would go dormant, and it showed no charge for around 2 weeks, then as if some one had flicked a switch, it started to charge, and the time on charge matched the Ah of the battery, and using the battery they seemed to be A1.

This was not done once, but with around 6 batteries, one proved faulty, but 5 were fit for service, varying from 7 Ah to 95 Ah. Most were AGM but at least one was flooded type.

Considering the results, it seems to make sense, if sulphur is left to harden over time, it will also take time to soften again. But until the smart charger we really did not have the option of leaving batteries for a long time on charge, it would have dried them out.

Colvid also presented problems looking after batteries, with cars sitting in drives for months, so the two Lidi smart chargers were doing the rounds, a week on each battery, the charger has 5 charging rates, 3.8A, 3A, 0.8A, 0.1A and off. Larger batteries once charged alternate between 0.1 and 0.8 amp, and smaller batteries 0.1 amp and off.

I again used the Energy monitor, and once charged you would see a good battery for example the nearly new battery in the Jaguar XE (AGM) switch off for most of the day and switch on same time every day for a short time, I assume some thing in the Jag was sending info to Jaguar at same time every day? But the older battery in the Kia, the charger was alternating between 0.8 and 0.1 amp too regular for my liking. This see hourly reading at top, I decided was not really good for battery, so would remove from charge when it did that, this however seemed to my mind OK, typical charging was like this and I would leave for a day at least on the very low rate of charge even when charger says charge is complete, to equalise the cells.

But as the battery gets older, if trickle charged the Ah seems to remain, but it holds the charge for less time, seems self discharge increases, I suppose to test one needs a load and a clock and a voltage switch, to record how long it takes before the voltage drops below a set figure. I would think running an inverter is likely the easiest way, as the inverter has auto shut down when the battery goes under a set figure, and the energy monitor would record not only the load but how long it ran for on the PC. But I have never bothered testing a battery that way.

 

[mattylad]

This reminds me I need to get a pair of new batteries for my daughters scooter.

If the charger is not supplying 27.6v (given that they are 12v SLA & in series) then it's not charging them correctly, 24v-25v will just not do.

 

[ericmark]

The voltage depends on how measured and how supplied, 12 volt RMS AC rectified is still zero to 17 volt, so it will actually over charge a battery. But rectified and smoothed it likely would not charge the battery. In the main today the 230 volt mains is rectified, smoothed turned into AC again at a much higher frequency, transformed down then rectified again, and smoothed, and a sample of the voltage is used to change the mark/space ratio of the high frequency AC to correct the output of the voltage required. Commonly called a switch mode power supply, which gives a reasonably stable output, this is very different to the old 50 Hz AC transformer.

The battery needs a reasonable high voltage peak to ensure cells are equalised, so a charger which switches off at 14.4 volt and back on at 12.8 volt, does a better job to a steady 13.4 volt. And the smart chargers from Lidi and Aldi when on offer are so cheap, it is hardly worth using a charger which is not a smart charger.

We have of course used stage chargers for years, but the three stages were high amps until 16 volts, then lower amps until returned to 15 volts then even lower amps until a set time has lapsed, which was OK for a flooded fork lift battery where you can top it up, but not any good for a sealed absorbed glass mat battery, also called valve regulated lead acid. Where over charging will destroy the battery.

I look at battery chargers offered for sale as being suitable for all lead acid batteries except absorbed glass mat, (AGM) and think then it's not suitable for all lead acid batteries, that all should be changed to most.

But testing has also changed, no longer can you use a hydrometer to work out state of charge, all we have is voltage, and with the Lidi battery charger it has a volt meter built in, and if you watch it then you will see the voltage rapid rise to 14.4 volt, then slowly decay to 12.8 and one realises it would need to be off charge for 24 hours before one could really use the voltage as any indication to state of charge.

So when I see the voltage at 12.2 yes I realise the battery needs charging, but at 12.6 it could have come off charge 5 hours ago and the charge cycle not completed and still only 50% charged, or come off charge 2 weeks ago and not far off fully charged.

So the only way is to charge for at least 24 hours before testing, this has always been a problem, back in around 1984 I was working in an auto electrical workshop, and we would have some one return a sealed battery as faulty, but until we had tried to charge it, there was not way to work out if discharged or faulty if the voltage was low. But the customer wanted a replacement there and then, if returned on the car, and car showed it was charging we could be reasonable sure battery faulty, but if just the battery returned, it was really guess work, and the owner was very reluctant to give a refund as if proved not the battery faulty, but just not charged, he was left with a second hand battery which he couldn't sell.

The voltage gave us a clue, but at the end of the day, it was a lot of guess work, I preferred at the time the flooded battery so I could use a hydrometer, some even had a hydrometer built in, with a sight glass which changed colour if charged or discharged.

But back then we did not have the option to use computer monitoring of battery charge level, and stop/start technology to save a egg cup of petrol/diesel, and the warranty for batteries used on taxi's and golf carts was only 6 months. When my mothers mobility scooter did 15 years on a set of batteries.

 

[dishman]

Just as a follow-up to this, I've been reading up on all things batteries.
I was curious to look at the options regarding using a Lithium battery in a scooter.
Specifically I was interested as to whether a lesser AH battery could be used to replace a standard lead-acid.

Lithium Vs Lead Acid - Marsen Energy

marsen.com.au

According to this site, that seems to be the case.

Based on what they say there, it is likely that you can get the same usable output for 50% less of the AH.

So, if I had a scooter with, say 2x32Ah batteries which apparently give a range of 20miles (give or take). Would I be correct in picking lithium batteries that were rated around 16AH?

Or, if I wanted to take a slight range hit, two 12AH lithium batteries.

2 x 12v 12ah Lithium Mobility Scooter Batteries + Charger Bundle | SLK Mobility

Get a pair of 2v 12ah Lithium Mobility Scooter Batteries with charger. Give your scooter the power to go further. Free next-day UK mainland delivery!

slkmobility.com

Or are there other factors to consider when looking at lithium batteries.

Also, out of interest, from that article it seems to say that standard lead acid batteries need to be charged at 50% depleted to avoid damage. So when manufacturers quote range on their scooters, are they quoting for that 50% depletion or until the battery is totally depleted and the scooter can't move.