Leisure battery testing - how?

[ChrisUK]

With a car battery a garage can do a high current discharge test, but this is not applicable to a caravan battery. So is there a way to analyse the state / capacity of a caravan battery? I have an approx 10 year old 85Ahr one that is probably / certainly past its best, but also a 110Ahr battery that came with the van that is only 26 months old. This newer battery I feel has never performed well on our extended non EHU stays in Scotland, but then our 2008 van seems to use battery power for everything. We are using very little lighting (currently it bearly gets dark here on Mull) and no TV / radio (no reception) but the volts still go down to below 12.2 after about 2 to 3 days. Last time I checked before we came away I only had a leakage current of about 13mA which is probably the alarm system.

So is there a definitive test?

 

[C_374479958]

Basically, the 2 batteries i.e the car and leisure are the same with slightly thinner plates and more of them in the car battery.

the tests are thefore the same and will do no harm in using a 'volt drop test' on the leisure battery.

 

[Peter_374382745]

The only way I check is is to completly charge and then discharge into a known load say a 12v car bulb of known wattage and current,Measure the dischage current anyway to confirm and see how long it takes to discharge to get a amp per hr result.

12.7v is 100% charged so battery must be at least this figure to start test.

12.4v is 75% discharged

12.2v 50%

12.0v 25%

11.9v 1.5% remenber these figures are on load NOT OFF.

By the way I check my car batteries using this method ,dont go the garage way as this only tells you the max current for a few seconds.This is only useful to see if the battery will discharge at a high current ie to start a car but using leisure batteries your not interested in this anyway...

If i get somewhere near 75% of battery rating ie 85a/hr then I am happy... less than 50%then do a pulse charge if you hav'nt already done one,and repeat test.less than 50% a/hr rating.... bin it,

 

[ChrisUK]

Thanks Peter I will have a go at this when we get home. Last time I had a car battery checked they didn't use the old big resistor load check, but some kind of hand held computer which was not big enough for a high wattage resistor.

Each year we do this long non EHU holiday so must get sorted before next year. Sound batteries will be the starting point.

 

[waffler]

Interesting I found my new van ran out of power quicker than the last. Found the fridge taking a lot even on gas just to run the electronics. I use a maplins volt meter to check state and change battery at about 12.3 volts- i found that after this is looses volts very quickly. Have you checked the fluid level? Found mine was too low.

 

[ChrisUK]

Back from hols now, I fully charged my old battery, then left it for 24 hours, then put a 4.6 amp load on it for 4 hours = 18.4 AHrs. I left the battery with out a load for a few hours and then measured the volts at 12.45 which I believe is 75% charge. Does this mean then that the capacity is 18.4 x 4 = 73.6Ahrs. This seems to be too good for an old 85Ahr battery.

Am I doing my sums wrong?

 

[JeremyClarksson]

12.45v seems low for 75% charge perhaps it is 75% discharge.

We do a lot of rallies use LED lights and have the TV on for up to 8 hrs and a 110Ah battery will comfortably last a weekend.

General rule for us is avoid using anything on battery that generates heat or uses fans - i.e blower, coolboxes etc.

Our biggest consumer is definitely the TV, personally I would leave it at home.

 

[ChrisUK]

you have spotted my error, 75% discharged. This gives me a capacity of 25Ahrs which is much more likely. i.e. I need a new one!