Thread: AGM Battery Charging

I'm certainly no expert either, but my view is that batteries in 4wd's are always a compromise, and never going to last as long as what you could achieve in a non-mobile installation.

Heat, deep discharge, vibration and not keeping them topped up when sitting for long periods I'm convinced do more damage to a battery than a couple of tenths of a volt off a perfect charge voltage will.

Steve

Originally Posted by Franz

Different battery types require differing charging voltages as can be seen from this Projecta 15A charger manual.

I have Optimas and it says 13.65 to 15.0 volts, no amperage limit. I trust the battery manufacturer more than the charger manufacturers.

Originally Posted by drivesafe

Hi Frans and the I personally would not use Gel batteries in any RV situation. They are just not suited to RV applications.

But even where Gels have been used, I have never heard of anybody having any sort of problem with overcharging them when they are fitted in a camper trailer.

As far as AGMs go, older AGMs had a maximum tolerance of 14.4v but most AGMs today have a tolerance of 14.7v.

Hi Tim,


Why do you think the GEL's are unsuitable for RV applications?

I only use my good old fashioned alternator to charge my 100Ah AGM battery. After 3 days of use I can tell you the poor old alternator gets a good workout for the first half hour back on the road...

It takes a bit to bring it right back up to full charge, but I've found 2 to 3 hours does it fully from a low charge. If its not 100% when I get home, I stick the solar panel back out for a day to top it off.

Just got back from a few days up the bush. It was at 11.85 volts (around 35% SOC) after 3 days in the one spot - running a 38 litre fridge and some LED lighting) - with pretty crappy weather, so the solar panel wasn't doing much. 1 and a quarter hour trip home and it is at 12.45 volts (around 85% SOC).

That's from an old fashioned Bosch 55 amp alternator that maxes out at 13.8 volts.

Originally Posted by Franz

Hi Tim,


Why do you think the GEL's are unsuitable for RV applications?

My only guess would be that they won't accept a large charging current like an AGM battery will. I would think without driving a loong way each day you wouldn't get enough charge into them? Only guessing here mind you.

Originally Posted by Franz

Why do you think the GEL's are unsuitable for RV applications?

Hi again Franz and for the very reason you pointed out, they have too low a maximum voltage level.

I have heard people who should know their stuff argue that for vehicle use the old wet cells are the best choice because the GELs and AGMs are overpriced for what they do. They argued it was better to pay less for wet cells and accept they might not last quite as long, but you could afford two of them for the price of one AGM.
Last time I had to replace the wet cell in the camper I looked at AGMs, but I could get a wet cell for $160 whereas the AGMs were around $300 and I just couldn't justify the extra cost. Plus the camper battery is charged through DC-DC and 240 volt multi-stage chargers so that's some protection against overcharging.
What do you think?

Sent from my GT-P5210 using AULRO mobile app

Hi DiscoMick and you are far more likely to get overcharged house batteries when you use a DC/DC device and/or battery charger.

With tens of thousands of my customers using nothing but the alternators to charge the house batteries, when towing a camper trailer or caravan, I have never heard of one of them over charging house batteries.

But there are plenty of cases of runaway battery charges cooking house batteries and the is a known problem that can occur when running a fridge off a battery that is being charged by a DC/DC device.

The problem occurs when the fridge cycles on, causing a small voltage drop, which then cause the DC/DC device to carryout a boost cycle.

These boost cycles are time oriented and have nothing to do with the SoC of the battery. So they just keep repeatedly over charging a fully charged battery.

This situation can repeat itself all day long and when you get to your destination you find you have cooked batteries.

This problem is so commonplace that a number of the installation manuals for different brands of DC/DC devices actually info the installer/operator not to power a fridge from a battery being charged by that DC/DC device.

Again, never heard of an alternator cooking house batteries.