Mobility Scooter battery, which one...

[dishman]

I took all those readings from the the three prong charging port on the scooter itself. In this case, it is situated on the neck of the tiller.

In the days that have followed, from only a rough estimation, it seems these batteries have struggled to provide more than 5miles or so before starting to indicate charging is required. Meaning on the display of LEDs one of the two green LEDs has gone out. At one point it even dropped to yellow after seemingly light use.

The batteries provided are from a reputable company and were brand new.

From what I know of this scooter's spec. The two 36ah batteries should provide around 20miles of range before needing charging.

 

[Harry Bloomfield]

I took all those readings from the the three prong charging port on the scooter itself. In this case, it is situated on the neck of the tiller.

Not an accurate place from which to measure true battery voltage, there could be considerable volts drop measured there, when the wiring under any sort of load.

As already said, your meter needs to measure the voltage when connected directly across the batteries.

The scooters own battery state gauge, is only accurate/only worth reading, when the scooter is turned on, but not moving. When moving, the volts drop will make the reading absolutely meaningless.

 

[dishman]

I located the only points I can see coming directly from the two battery caddies, there is a junction where two positive and two negatives meet a connection bridge where the rear of the scooter detaches (it's collapsible).

I get a voltage reading when connecting the multimeter to one of the positive and one of the negative points.

It reads around 25v (as I would expect) after a full charge, however if I try to take a reading with the scooter moving, it briefly (less than a second) drops about a volt, and then further drops to zero. But this must be for another reason as the scooter runs fine.

So now I am confused about how to get a consistent voltage measurement that will indicate the actual health of the battery.

 

[dishman]

Any thoughts of the best points to test these batteries, and to assess their condition. Is the voltage drop when the scooter moves due to the fact they are in series or something. Just trying to get my head round why the reading would drop to 0.
The multimeter I am using is a decent one, so should not be getting erroneous readings.

 

[ericmark]

I would measure as shown at the battery, mine at the moment have the boxes open so I can charge without taking the scooter into the house. Also need to replace the overload in battery to right, on my to do list.

 

[dishman]

I guess I can run the caddies without the lids.

I would then see the voltage drop across each battery when used, and what, it should not drop below 12.4? Something like that?

 

[Harry Bloomfield]

Any thoughts of the best points to test these batteries, and to assess their condition. Is the voltage drop when the scooter moves due to the fact they are in series or something. Just trying to get my head round why the reading would drop to 0.
The multimeter I am using is a decent one, so should not be getting erroneous readings.

The only place, to measure the voltage of any battery, which is under some loading, is at the actual battery terminals. Anywhere else, will suffer a lower reading, due to volts drop.

 

[dishman]

OK...the results, and they are....interesting to say the least.

I took the caddy covers off and measured voltages on each battery directly with the scooter moving. I had to hold it while moving but I think I got stable enough readings.

I would like some opinions on initial interpretation though...

So...

New Batteries - fresh charge

Initial voltage with scooter off: (fresh off a charge)
B1 13.11v
B2 13.15v

B1 (moving slow) 12.72 - 12.75
B2 (moving slow) 12.72 - 12.75

After that run I tested the batteries off again
B1 12.97
B2 13.02

B1 (med/fast pace) 12.65 - 12.7
B2 (med fast pace) 12.67 (ish)

Old Batteries - recently charged

Initial voltages (scooter off)
B1 13.04v
B2 13.01v

B1 Slow 12.88
B2 Slow 12.72

I then measured a second slow run

B1 (slow) 12.71
B2 (slow) 12.67

Batteries at rest again (scooter off)
B1 12.91
B2 12.90

Run 2 med/fast

B1 12.59v
B2 12.59v

So, does this indicate that the old batteries, while a bit worn are certainly still in decent condition with plenty of life?

It looks like the new batteries recover their initial voltage quicker perhaps.

Thoughts?

 

[Harry Bloomfield]

OK...the results, and they are....interesting to say the least.

I took the caddy covers off and measured voltages on each battery directly with the scooter moving. I had to hold it while moving but I think I got stable enough readings.

I would like some opinions on initial interpretation though...

So...

New Batteries - fresh charge

Initial voltage with scooter off: (fresh off a charge)
B1 13.11v
B2 13.15v

B1 (moving slow) 12.72 - 12.75
B2 (moving slow) 12.72 - 12.75

After that run I tested the batteries off again
B1 12.97
B2 13.02

B1 (med/fast pace) 12.65 - 12.7
B2 (med fast pace) 12.67 (ish)

Old Batteries - recently charged

Initial voltages (scooter off)
B1 13.04v
B2 13.01v

B1 Slow 12.88
B2 Slow 12.72

I then measured a second slow run

B1 (slow) 12.71
B2 (slow) 12.67

Batteries at rest again (scooter off)
B1 12.91
B2 12.90

Run 2 med/fast

B1 12.59v
B2 12.59v

So, does this indicate that the old batteries, while a bit worn are certainly still in decent condition with plenty of life?

Yes, both seem reasonably OK.

 

[Scally-Ho]

You have to remember that traction batteries are 'deep cycle' so perform differently to others.

 

[dishman]

After a short recovery time:

New Batteries
13.11v
13.16

Old
12.96v
12.97v

So both recovering, old just a bit slower than new.

You have to remember that traction batteries are 'deep cycle' so perform differently to others.

But, do those readings suggest both batteries are performing well for deep cycle?

Or should I be using another way to assess them?

 

[Harry Bloomfield]

You need to measure them again, after doing a few miles.

 

[dishman]

Ok, I did a 3 mile test. I did 6 laps on a half mile circuit and did a reading on each lap:
It wasn't all on the flat, but as it was a circuit it had equal uphill and downhill.

Lap 1: 12.74
Lap 2: 12.72
Lap 3: 12.69
Lap 4: 12.65
Lap 5: 12.61
Lap 6: 12.61

After all these laps I did a voltage check while going at 2mph on the flat and I was getting around 12.55v

At the end of the 6 laps the light display on the scooter was reading orange while in use.
After pausing and resetting after each lap it usually went back to full green, but by the sixth it dropped one light.

Thoughts on that result?

 

[Justin Passing]

I think to measure the batteries' "condition" you'd have to run them until you get a voltage indicating "flat", and time it.
Your numbers indicate you're still inthe "not flat yet" part of the discharge curve.
The internal resistance would go up with age but at 0.1V at 4Amps it's 25mOhms, not a problem I think.
It would vary between battery designs of course.

There's a graph and some chat here https://electronics.stackexchange.c...-of-a-lead-acid-battery-drop-with-load#450518

If you need a meter you could add one of this sort of thing https://www.ebay.co.uk/itm/187423176262 - and use for charging your phone

 

[dishman]

So I did a bit of a follow-up, and did another 6 laps 2days later (without recharging), and the results were interesting:

Initial voltage after recovering for 2 days was 12.78v

Lap 1: 12.54
Lap 2: 12.5
Lap 3: 12.44
Lap 4: 12. 41
Lap5: 12.36
Lap 6: 12.29

So there was a steeper drop off for the second run.

I then put all this data into cGPT and it crunched the numbers.

It's basic summary was that based on those voltage drops, which were consistent and in line with expected curves, and based on the distance I covered, at 50% discharge I could get about 9 miles out of these batteries.

Doing this as certainly helped me understand how the batteries are depleted much better.

Also, i know know how to read the display better. As someone mentioned, it not useful as a live read-out. But is useful on initial turn on after a short rest to give a good indication.

After 7 miles, after a stop and reset it was showing one green light out. Another 2 miles and I would expect the second green light to go out and that would indicate a 50% dod and when it should be ideally be charged back up.