Batteries

Kevin 1955 · Veteran Member

Batteries

Phil C · Guru

Hi Kevin and welcome to the forum.

I'm told these AGM batteries will tolerate an occasional low voltage, rule of thumb is not to take them below 50% which, arguably is about 12.7 volts, that depends on who you talk to. If they are taken low all the time their life will be significantly shortened.

Bottom line is yes they should be OK, I would urge you to get a small ctek charger to keep them in condition, or even better, leave the van connected while at home.

Cheers

Hylife · Guru

I am sure there are many knowlegable GNs who know all this stuff, but not everyone does, so purists and pedants please forgive me as I put this in somewhat simplistic language for the average Joe (or Jean) to understand.

Regardless of the contruction method of the battery, wet, gell, agm, etc, most lead acid batteries will self discharge at a rate of up to 1% per day.

During the discharge process the sulphuric acid (H2SO4) deposits sulphate (SO3) on the lead plates leaving water (H20). The recharge process reverses this. Look inside an old wet battery and you will see this white powdery muck all over the plates, sulphate.

If the sulphate coating gets too thick the recharge cycle cannot get sufficient access to the lead plates and therfore cannot completely reverse the process. In a normal car battery as little as half a dozen times leaving your lights on to TOTALLY flatten your battery can kill it permanently. Car batteries are designed to remain completely charged all the time with only a very short high current drain by the starter motor. The modern car alternator puts out anything from 80 to 150 amps, sufficient to quickly top up your battery and to power all your car's lights and accessories without drawing down further from the battery.

Deep cycle batteries have extra quantity and sized lead plates to prevent this excess sulphation issue (it's why they are really heavy), however, every charge process minutely breaks down a small amount of lead from the plates which ends up as slush on the bottom of your batteries cells. The more deeply you discharge your batteries the greater the lead breakdown on recharging and therefore the shorter the lifespan.

The majority of quality brands would offer up to 1500 cycles for a 25% discharge reducing down perhaps as few as 300 cycles for a 50% discharge.

Most manufacturers on their web sites will provide discharge rate Vs life cycles for their batteries.

Peter_n_Margaret · Guru

Hylife wrote:
Regardless of the contruction method of the battery, wet, gell, agm, etc, most lead acid batteries will self discharge at a rate of up to 1% per day.

Some are clearly better than others.

AGMs were originally designed for the military and the requirement was low self discharge in seldom used military equipment.

At least 9 months is considered normal, providing all loads are completely eliminated.

Storage temperature also has a marked effect on the self discharge rate. The warmer they are, the greater the self discharge.

I had wet cells (never my first choice) in the MH we used in Europe for 3 years. It was left in storage for over 6 months each winter (in a farmer's shed in the Netherlands) with both the crank battery and the 2 house batteries disconnected.

There was never a problem starting the vehicle or getting things going again after that time.

Cheers,

Peter

iana · Guru

Hylife, that was an excellent reply to the question. Thanks for taking the time and effort. I learnt more!

PeterD · Guru

Hylife wrote:

If the sulphate coating gets too thick the recharge cycle cannot get sufficient access to the lead plates and therfore cannot completely reverse the process. . snip

Deep cycle batteries have extra quantity and sized lead plates to prevent this excess sulphation issue (it's why they are really heavy), however, every charge process minutely breaks down a small amount of lead from the plates which ends up as slush on the bottom of your batteries cells. The more deeply you discharge your batteries the greater the lead breakdown on recharging and therefore the shorter the lifespan.

I think that is a statement that needs challenging. Sulphation does not occur on the surface of the plates. The battery operates by the lead and lead dioxide in the plates changing to lead sulphate during discharge. Recharging the battery reverses the process. However if you don't recharge quickly enough the sulphate crystals harden and will not revert during recharging, this hardening of the sulphate is what is referred to as sulphating.

See this link, it explains things better. While you are there you may care to read the whole article and find out how batteries work. That may help to counter all the BS written about batteries in these forums.

This link explains the real difference between the different types of batteries. The size of plate has little to do with sulphation, the thickness of the plates however does have a bearing on the percentage of the plate material that falls off during use.