David Lock

I have retrieved a pair of 12v 40Ah batteries from a mobility scooter and now want to find out if they have some life left in them or need replacing. I've had one on charge for several hours and charge needle is a bit past half way mark on charge indicator.

So can I buy something on ebay which will give me a better idea if they are any good? Sealed units btw.

Thanks, David

jaygsi

iTrader: (46)

Yes you need something that puts a load on the battery. I have something in the garage.

David Lock

OK, thanks. But how is that going to help me?

dl

dpb

Volt meter, 15 quid from anywhere

Should record 13.56 roughly when fully charged , sounds about right so far

Should be deep cycle

David Lock

andy97

iTrader: (1)

Modern chargers- Ctek and alike will charge a battery upto 13.6V. The quicker this happens the more optimistic you can be about the battery performance.

Without a load test its a little bit of judgement. My method to ensure my batteries are in good order. Charge with a decent charger till its says fully charged. Then disconnect battery and leave to stand for a few days. Measure the voltage it should have more than 12.5Volts. If it does, good battery, if its <12.5V suspect and if <12Volts poor battery, especially if it turns cold.

johned

You might get the volts reading but you really need a drop test(load).

David Lock

OK guys thanks. I've learnt quite a bit about batteries in the last 24 hours especially with help from a company called Pitstop. Batteries for mobility scooters are dry cell sealed and very different from batteries I am used to for cars. They need very regular charging to keep them going and I think the ones I had had been left for too long without a charge. My dilemma was to determine whether I should just get new ones but they are about £90 each hence my post on here. The only way to properly test them was to check them with a Capacitor Testing thingy but these cost circa £500 so I backed off that one

David

dpb

So presumably they aren't deep cycle...?

David Lock

Well I believe they are deep cycle but not 100% sure. d

These are what I got but they are physically too big to fit so I have to return them.

Product Quantity Price
12V 50Ah BBB Sealed Lead Acid (AGM) Mobility Scooter Battery
2 £163.98 (ex. VAT)

dpb

If they are deep cycle, they can take a lot more abuse /running down than car battery !

David Lock

With respect - not true

d

dpb

http://www.batteriesinaflash.com/deep-cycle-battery-faq

David Lock

Fake news

(but thanks). I'll take a week off to read through.........

d

dpb

Trumps going solar for his wall, and its all his own idea


There's plenty here that will lap it up

ALi-B

iTrader: (1)

Capacitance testers aren't all they are cracked up to be; they only test peak output and do not really test Amp-hour capacity. We have a expensive Midtronics tester and I've proven that's its only good for quick and dirty testing; For batteries that are boarder line the results are unpredictable; Duff battery that still gives out good peak amps (cranking amps) can show up as a pass, same with batteries that suffer a slight internal discharge.

Plus you don't need expensive equipment to test. Just time, a proper intelligent charger (the fact you mention "needle" would imply you have a basic dumb charger which in itself can wreck a battery), a dummy load and a multimeter.


Right 40Ah battery is 1amp for 40 hours or there abouts.

So fully charge it, preferably with a Ctek or similar. Disconnect charger. Check voltage; should be over 12.8v for a AGM battery. Now leave it disconnected for about 30mins to allow surface charge to dissipate. Then measure voltage; It should be around 12.8v. Minimum 12.6v. Any lower, it has a faulty cell(s) or wasn't fully charged. Charge it and try again, bear in mind some chargers don't always charge properly or maybe faulty and if using a dumb charger you are just playing guesswork.

Now leave it overnight. Then re-measure voltage; It should not drop any more than 0.1v, if it has, there maybe an internal short. Leave it for another 12hrs or so and re-measure. If the voltage had dropped further, it's junk. If Ok, proceed to the next test.

Now to test its capacity:

Connect a known load, say a car headlamp bulb which is 55watts or about 4.5amps (confirm with Ammeter). A new fully charged 40Ah battery should power that bulb for 8.8 hours. (4.5 into 40 is 8.88889). But you shouldn't fully discharge the battery as that does damage them: aim for 75% of its capacity. The voltage at 75% discharge for a AGM battery is 12volts (disconnected after resting for at least 20mins).

So for a 40Ah battery 75% of its capacity is 30Ah which means for a 4.5amp load should give you 6.6667hours before the battery drops to 12v (after disconnecting and resting for 10mins ). This would be for a brand new battery.

The healthier the battery the higher its capacity (the longer the bulb stays lit) Lead acid batteries loose capacity with age or if sulphated from being left with it below 12.4volts
So for a old aged battery, I'd expect 4 to 5 hours for a serviceable battery. For a battery that is past its prime would give less than 3 hours. Obviously if it only gives a hour or so, it's junk. Even so it may give good peak Amps, but the capacity is too low to be of any real use.



My Golf has a 100Ah AGM battery...it's almost 12years old. It still has very good peak amp output (cranking amps) hence it'll start the car no probs even after leaving it for two weeks, but its capacity is probably less than half its original rating as can only run my car Hi-Fi (Alpine PDX-F6) at nominal volume for 60mins..any longer and I won't have enough power left to start the engine. Rough maths makes its capacity 41Ah...I doubt it'll get me through next winter The Midtronics tester failed it donkeys ago but still show it has a very high cranking amp rating.

I can highly recommend Enersys Genesis AGM batteries; our jump pack uses these ( also used in golf caddys and scooters) and have had some severe abuse, certainly worth the extra over generic no-name brands.

David Lock

My brain is hurting

Well I've bought a pair of new batteries. All I want to do do is to get down to the local without stopping

I'll report back or be arrested for drunk in charge of a cripple scooter

I really appreciate the comments from you guys btw.

Cheers (I hope)

David

ALi-B

iTrader: (1)

Cool beer was my motivation to learn about batteries; I tend to stock pile old large capacity batteries for camping to run my cool box; Found conventional testers didn't work for me; After finding warm beer halfway through a weekend when the battery "should" have run it for the entire trip.

Did devise a 12v DC to 15v DC supply to charge the cooler battery off the car battery without needing to run the engine. Unfortunately anything above 10amps became quite costly.

johned

All is well that ends well good luck and enjoy the drink.

ditchmyster

iTrader: (7)

Good man, now that's a proper reason... 'Pub Rollerskate'