7 Ah lead acid sealed battery advice please.

[ericmark]

My mother has a stair lift suspected battery changed and proved correct. So now left with two 7 Ah 12 volt batteries which show as being fully charged but voltage drops too low to work stair lift.

When I tested I found trying to use the lift increased the time before battery failure each time I tried to use it. I feel fault likely caused through lack of use and likely one can revive the battery to some extent.

As to stair lift not worth taking a chance but with the pedestrian controlled wheel chair should the battery fail easy enough to lift power wheels and carry on simply pushing it so worth trying to use battery for wheel chair. Two in parallel should do the job nicely.

So is there a way to revive the battery to some extent? The battery charger just says charged. Will guess valve regulated absorbed glass mat type. Fact they were mounted on their ends makes me think not a standard wet battery.

Seems a shame to just bin I am sure I can get some more life out of them if only to run my radio.

 

[Burnerman]

Investigate 'smart chargers'.....they may recover your battery to some degree.
Its not a good move to have one good and one poor battery in parallel though, so if it doesn't recover its off to the recycling centre.
John

 

[ericmark]

I think my Lidi charger is a smart charger and since it was 24 volt in stair lift putting in parallel instead of series means should be two poor batteries in parallel not one good and one bad. I know the larger battery both vehicle and traction and in the main keeping fully charged on float they will last many years it is keeping flat which causes the problem.

But these have lasted just 4 years with hardly any use where last set lasted much longer with regular use so it seems these batteries must be discharged and recharged to last.

It may be running flat and recharging will get them going again but it also could wreck them. I have no experience with AGM batteries. 4 years seems a very low life I would have expected 10 years with standard lead acid under same conditions. Could be I need to run the chair lift every month to make batteries last or some other action.

I just hope to learn more about this type of battery.

 

[Burnerman]

Batteries tend to like an easy life for best performance - which means they should never be allowed to become flat or be overcharged.
The battery packs in the Toyota Prius hybrid are proving to be very reliable due to this technique - they are actually exceeding expectations.
John

 

[DrJimFranklin]

If batteries are allowed to discharge very slowly via the atmosphere then this can cause damage to the plates. This has been known for a very long time. Modern batteries are designed for the purpose they are put too. Some are designed for deep discharge cycles with a fast recharge, some a designed for modern discharge and slow charge..etc etc.

The chair lift requires 24V dc, that must is apparent from your post, and the 7Ah batteries you have or US after 4 years of intermittent use. As batteries only have an average life expectancy of around 4 years anyway I would suggest that one or both has simply come to the end of thing naturally, perhaps a little rushed by the manner of it's use.

My suggestion would be to buy two new 12Ah batteries and use a CTek battery conditioner/charger when the chair lift is not in use. These are great chargers and the recondition batteries. If the current batteries are not holding a charge then you may be able to recover them with a CTek. I personally use a CTEK Mulit MXS 5.0 to maintain the batteries for my Land Rovers, alarm systems etc..It even recovered a battery that was 7 years old, had sat doing nothing for 5 years and was so bad it would not charge...it now powers my Discovery no problem.

 

[ericmark]

My daughter has my meter but I seem to remember battery was floated at 13.8 volt which seems about right. As an auto electrician I learnt about lead acid batteries but the AGM was not out in 1980 when I moved to low voltage and left extra low voltage behind. My son tells me alarm batteries don't last too long either and I wonder if these batteries are really suited to stand-by application?

However all I read about AGM seems to say better than old wet cell so why such a short life? The chair lift stops working when voltage drops to 20 volt under load which it states is 0.26 kW so around 10 A (overload comes in at 18A) which is quite heavy for a 7 AH battery but not OTT. A car battery if looked after will last around 7 years so these batteries it seems are better than standard car battery so I would expect 10 years. Two sets of batteries failing premature makes me wonder why.

 

[DrJimFranklin]

AGM batteries of the 7Ah range are designed for standby support for alarm panels, and smoke vent applications, that type of thing, They are not designed for sudden heavy current drain.

Stick with lead-acid for this, for your needs I would recommend a Yuasa NP12-12 Lead Battery 12V. This is a 12Ah 12V lead acid battery that is designed to be used for motorised systems and is often used for in electric vehicles (small ones obviously). These costs from £22 to £30 depending supplier. You can even by them from Amazon. I strongly recommend an a high quality conditioning charger be used with them. They will last a very long time then.

 

[ericmark]

Not a CTek but a Lidi charger of similar design. The chair lift has a two stage charger. I must check the size of battery fitted to wheel chair. More than 7Ah but not sure what size. It was left flat for couple of years and is now only good for around 1/2 mile but each time used it seems to get better. My thoughts were I only need around a mile not the 10 mile they are designed for and if the old chair lift batteries will give me the extra then great.

 

[FDJ]

So is there a way to revive the battery to some extent?

I recently tried to revive a large number of ex-UPS batteries that were showing similar symptoms.
I added water to each cell and at first, the results were encouraging.
However, every single one suffered another type of failure. Probably internal cell collapse and none were usable.
These things are built down to a price nowadays and barely last their expected life.
If run at anything over 20C, their life is reduced considerably.
FRANK

 

[ericmark]

Years ago I tried to add water to sealed batteries, Now I realise this was an error once seal is broken then valve becomes useless, for one it allows oxygen into the battery which will destroy it. What I can't understand is how using the stair lift seemed to extend how far it would travel with each use. The old NiCad cell was known for having a chemical memory but this was not something associated with lead acid cells. Yet it seemed these valve regulated absorbed glass mat cells behave similar to the old NiCad cells. However manufacturers say they don't have a chemical memory.

There are a few things which have come to mind including position of battery when in use. It states using upside down is not recommended but it seems using on end or side is OK. One wonders if the batteries were simply removed and refitted standing on opposite end would this improve the performance?

Reading about the batteries it seems the limit to discharge is amount of acid not amount of lead so they can't be over discharged. Manufacturers seem to quote between 8 and 20 year life for VRLA cells, but the stair lift seems to only get 4 years out of a battery. This points to something being wrong. The batteries in the mobility scooter are at least 10 years old and still going strong. They were poorly treated when my sister took the scooter without charger and stored in her garage for a year without charging.

The pedestrian controlled wheel chair was also poorly treated with the battery being allowed to become flat and remain flat for some time. Again using the chair each discharge and re-charge seemed to improve the batteries performance.

All in all experience seems to show non use be it charged or discharged seems to damage the battery and it would seem they last longer when used. I have many items that use 12 volt batteries and from this it would seem sharing battery may be good for the battery. So same battery used to cut hedge in summer and radio in winter seems good.

However this does not seem to match what manufacturers say. Only description I have is "Maintenance-free. Computer-designed lead, calcium, tin alloy grid. Long service life, float or cyclic applications. Low self-discharge." and "Sealed Lead-Acid Battery 12V 7Ah 100 x 65 x 151mm" it does not even say if gel or absorbed glass mat but I would assume the latter.

It could be of course the original batteries and first replacement were not new. We have no idea how long batteries are stored before we get them. One hopes Screwfix has a good turn over so not left in stock too long.

 

[SimonH2]

AGM batteries of the 7Ah range are designed for standby support for alarm panels, and smoke vent applications, that type of thing, They are not designed for sudden heavy current drain.

Stick with lead-acid for this

Err, AGM batteries are lead acid And many (most) of them are very much designed for short heavy loads - such as computer UPSs. In fact, if you compare specs, AGM tend to out-perform "wet" (aka flooded cell) batteries which is what I suspect you may be meaning when you say to stick with lead acid. AGM batteries actually tend to be much better for short term high discharge rates - they have a lot of thin plates (lead tissue) which gives them a massive plate surface area which supports a high discharge rate without "losing capacity" in the same way a wet cell, where the bulk of the plate surface area is in the pockets of paste, does.

It is certainly true that you can get the same performance from wet cells, they tend to be a lot heavier - and you have to deal with the hazards from acid spillage and hydrogen generation.

I did look into switching to wet cell for the main UPS at work. We don't have the luxury of having battery storage in an artificially cold space, and that impacts on AGM battery life - whereas wet cells can be easily topped up to compensate for the loss of water. I concluded that we'd need to shell out a lot more than we had budget for (lack of reasonably priced "small" batteries) and we'd have to deal with the aforementioned hazards of having "wet" sulphuric acid and hydrogen about. Also, unlike AGM "dry" cells, you do have to cycle wet cells periodically or the acid tends to stratify (the denser parts settle at the bottom).

Under "good" conditions, 4 years isn't a poor life for a typical AGM battery. Most respectable manufacturers provide (in amongst loads of other stuff) graphs of typical life vs temperature. At typical "home" temperatures, especially the slightly higher ones often found where infirm people are living, then 4 years is about what I recall having seen from the graphs.

 

[DrJimFranklin]

Simon, of course they are, but your average Joe on the street does not understand the difference between AGM units and conventional "Lead-Acid" batteries. They do not call them AGM and Flooded cell in the shops and most people would not have a clue...so I stuck with generic terminology for clarity. However if you want to know about batteries I can provide a little background for you, and this will explain why small AGM batteries are not the best solution in the power range being discussed.

AGM technology became popular in the early 1980s as a sealed lead acid battery for military aircraft, vehicles and UPS to reduce weight and improve reliability. The acid is absorbed by a very fine fiberglass mat, making the battery spill-proof. This enables shipment without hazardous material restrictions. The plates can be made flat to resemble a standard flooded lead acid pack in a rectangular case; they can also be wound into a cylindrical cell.

AGM has very low internal resistance, is capable to deliver high currents on demand and offers a relatively long service life, even when deep-cycled. AGM is maintenance free, provides good electrical reliability and is lighter than the flooded lead acid type. It stands up well to low temperatures and has a low self-discharge.

The leading advantages of AGM are a charge that is up to five times faster than the flooded version, and the ability to deep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other hand, is specified at 50 percent DoD to attain the same cycle life. The negatives are slightly lower specific energy and higher manufacturing costs that the flooded. AGM has a sweet spot in midsize packs from 30 to 100Ah and is less suitable for large UPS system.

AGM batteries are commonly built to size and are found in high-end vehicles to run power-hungry accessories such as heated seats, steering wheels, mirrors and windshields. NASCAR and other auto racing leagues choose AGM products because they are vibration resistant.

AGM is the preferred battery for upscale motorcycles. Being sealed, AGM reduces acid spilling in an accident, lowers the weight for the same performance and allows installation at odd angles. Because of good performance at cold temperatures, AGM batteries are also used for marine, motor home and robotic applications.

AGM is also making inroads into the start-stop function of cars. The classic flooded type is simply not robust enough and on repeated cycling causes a sharp capacity fade after two years of use.

As with all gelled and sealed units, AGM batteries are sensitive to overcharging. These batteries can be charged to 2.40V/cell (and higher) without problem; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell), and a direct replacement with a sealed unit could spell trouble by exposing the battery to undue overcharge on a long drive.

AGM and other sealed batteries do not like heat and should be installed away from the engine compartment. Manufacturers recommend halting charge if the battery core reaches 49°C (120°F). While regular lead acid batteries need a topping charge every six months to prevent the buildup of sulfation, AGM batteries are less prone to this and can sit in storage for longer before a charge becomes necessary.

AGM batteries are good for standby use due to their low discharge characteristics but you need to select the AGM battery for your needs. Some are designed for standby use and some are designed for "instant on" use with high current draw and then a recharge. The problem with using small AGM batteries for motorised systems of this nature is the discharge may be more than the charge cycle is able to replace effectively before the next use, this will damage the battery and reduce it's life. Correct battery selection is critical.

 

[SimonH2]

The problem with using small AGM batteries for motorised systems of this nature is the discharge may be more than the charge cycle is able to replace effectively before the next use

Indeed, and that will apply regardless of the chemistry/technology chosen. You have started off to explain why AGM are a bad choice for this application - then, with all due respect, rattled off a list of why they are actually a good choice. The only downside of AGM for this sort of application is their sensitivity to overcharging and elevated temperatures - which is simply down to the fact that they have very little electrolyte and so losing even a small amount reduces their efficacy.

Small, lighter, high discharge rate, and spillproof - other than the above mentioned sensitivites they win hands down

 

[DrJimFranklin]

Simon...AGM are better batteries..but you are conveniently ignoring the comments about selecting a battery designed for the use you intend to put it too, the fact that a flooded cell battery has a higher charge rate than an AGM battery is a plus for conventional wet cell batteries that means for the use intended they are a far better choice.

AGM batteries perform best with charge cspacities between 30Ah and 100Ah. The size you are looking at is between 7Ah and perhaps 15Ah...not the ideal range. If there is space to fit a larger 30Ah battery then choose an AGM, but if you are limited to the smaller units I would stick with wet cell units.

 

[SimonH2]

the fact that a flooded cell battery has a higher charge rate than an AGM battery

Really ?
Both charge and discharge rates are higher with AGM. Put another way, if your charger can supply the current, you'll get your bulk charge in a hell of a lot quicker with an AGM than with most wet cell batteries. Note that "if" there - a lot of kit has "basic" charging and that'll leave you with questionable performance regardless of whether it's a "dry" or "wet" cell.

But it's pretty well irrelevant anyway - the equipment is designed for that size and type of cell. It's highly unlikely to have physical room for a wet cell of similar performance, and I doubt the OP will want to re-egineer (starting with a lot of reverse engineering) the charging system to maximise performance for wet cells.