Battery capacity measurement (IBT-Gold)

For wet cells the specific gravity of the electrolyte tells you the state of charge.

State of charge isn't the same as capacity, as the total capacity of the cell falls with age - s.g. only tells you what proportion of this total you can still expect, not how big a pot might be available.

The claims for this gadget are clear enough, but it's hard to tell how accurately this "frequency response" technique maps onto actual capacity. You'd have to do 100s of long-term discharge cycles to know for sure, as they do indeed claim to have done.

Understood but very few batteries are wet and accessible these days (AGM / VRLA / recombination / whatever).

Ok and thanks,

T i m

Hence why I though this capacity meter was a good thing (assuming it reliably does what it says on the tin etc).

Indeed ... the terms they use in the ad could be bordering on snake oil if you don't understand them etc (not that I'm suggesting such in this case etc).

Yep.

I have plotted many a C20 discharge graph (when I was racing EV's) and it's quite surprising the difference seen between several batteries from the exact same batch. I would still be happy with such measurements (variations) taken with said gadget as long as it did actually reflect the current state of the battery.

Now given enough exposure to any particular spec battery (say SLI batteries as seen in a typical car garage) you could by using a DVM, ampere clamp, charger (better with an ammeter) and discharge doodar get a pretty good feel re the condition of a battery when presented for 'testing'. But what of those 'summer batteries' that are fine in summer but can't make it in the winter? Is it just capacity or could it be underrated for the task or the duty cycle / load?

All the best ..

T i m

I have one of the meters you link to, bought cheap(er) on ebay some time ago.

I've used it with gel-cell batteries as used in UPSs, car batteries and leisure batteries, and find it gives an accurate picture of the battery, and often confirms what I suspect for a battery strugging to start a car etc. Certainly a new battery gives a far heigher reading that an old one - seems the meter is doing what it should.

To me it's been a good 'investment', certainly useful to have in the garage.

Alan.

Ah, good ...

The sort of stuff I'd use it on as well, great.

Just out of interest, how closely does the thing measure the value of a new battery, once you have done any conversions etc? ie, Would a

Seem like it might need further investigation. ;-)

Cheers, T i m

Most car ones still are - if you peel off the top label. Then possibly remove some plastic covers. Underneath are the usual screw in plugs.

It's hard to say. I recently used it on an old car battery, which was struggling to turn over the engine even after an overnight charge. The battery's (original) capacity was 62aH, according to the label. The meter reported it at 22aH. The replacement battery was rated at the same capacity however the meter showed the capacity just under 70aH. I don't know if this is to be expected - that a brand new battery's capacity is higher than claimed. I suspect it will soon drop off after regular use to closer to the rated capacity.

Either way, the meter proved the old battery had had it, and took any doubt out of the decision to replace it (the owner refused to believe it needed replacing as it had only been fitted 1 year before!)

- It had been allowed to stand dischaged for several months which would have damaged it.

Alan.

So not convenient though eh and I'm not sure if that would affect how it works (the electrolyte recovery etc).

T i m

Ok, that sounds good.

I think they mention something about not taking a real measurement after the battery has just come off charge.

I think there could be several variables that could affect the measurement, like temperature and charge status as mentioned above.

;-)

It certainly would have done it any good.

The mate that gave me a 'very expensive' 10Ah SLA battery to play with mentioned that it had been 'standing for some time, only read about

I should have just thrown it in the bin at the outset (at the 7V point) but thought it might be worth a go.

The other 3 batteries he's since given me all seem to charge and function ok but I would really like to see what capacity they now are. No point keeping something supposedly rated at 7Ah if it's actually only now 1Ah.

Cheers, T i m

Doesn't harm to have a look - they're not pressurized or anything. But don't expect it to need topping up - unless you've had a long running overcharging situation.