[RedDevil]

Originally Posted by paulgato

Another conversation with Enersys UK tech support about Odyssey batteries. This time to find out why they require a minimum of 40% of the Ah rating as a charge current - in other words, a 100Ah battery will require at least a 40A charger. This I only found out AFTER buying the battery of course.

It turns out this is the case (so I will need to buy yet another charger!) and that charging at a lower than 40% rate will SIGNIFICANTLY reduce the number of cycles and the overall life of the battery. Conversely, there is no upper limit on the size of a charger provided the charge voltage is properly regulated. The battery itself will limit the amount of current going into it. Charging at a high current will have no adverse effect on the battery whatsoever. (The guy I spoke to had done some testing using an industrial charger capable of well over 1000A.) Another very useful conversation. It turns out the technology for these Odyssey batteries was developed in the UK by a company that was later acquired by the Enersys group.

So, I need to get another charger. Unfortunately powerful chargers will always have fan cooling, which means they cannot be waterproof, which means engine bay installation is not ideal. So I shall have to get another charger AND find another place in the vehicle to install it. (Maybe I should have a re-think. Maybe the Odyssey is not such a great choice after all and maybe I should return it. Maybe a supercapacitor array in the engine bay and two deep cycle 100Ah batteries in the rear is not such a crazy idea after all.)

...As to WHY the Odyssey batteries work so much better with a higher charge current, the guy I spoke to said there are different theories as to why that is but in truth no one really knows. They just know that IS the case in practice.

That is strange. I cannot see how charging on a low current could be bad for a battery, unless it is has a shorting cell.
What is known to limit the life of a battery is how deep you discharge it; dicharging beyond 40% SOC does indeed reduce the life of a battery; you can discharge a lead acid battery to 75% many thousands of times, but discgarging to say 10% will kill it within a few 100 cycles.
40% may well be the most economical point; beyond that the damage you do to the battery outweighs the benefit of prolonged running without alternator.
IMHO instead of charging it hard you might well focus on avoiding deep discharge.

To play devils advocate: if they get you to buy an expensive charger for your battery they make sure you will buy another like battery if it goes bad, or you would have wased all that money on the charger...
I would like to see proof that you do need a big charger for a big battery.
At least it does have the benefit of fully charging your battery within a few hours, but that's it.

I have restored some dead batteries to more or less full capacity by trickle charging and short bursts of discharge. I do have an OptiMate4 desulphating charger that does that automatically for motorcycle batteries (it could not cure my car 35Ah battery btw; it had a shorting cell). The thing to avoid there is high voltage; if the battery does not take the current it is essential not to push it by raising the voltage.
My charger could output no more than 1 Amp.