Outer Limits 4x4 Board

Hello,
is it okay to charge a deep cycle battery from the alternator or is there a better way/ intermediate protection of overcharge between the vehicles alternator and the deep cycle battery?

Thanks

Hi jedipi, it depends on the type of deep cycle battery.

If it’s a standard flooded wet cell deep cycle, the ones with filler caps on the top of them then you can charge them straight off the alternator.

If it’s an AGM type then unless it is specifically designed for automotive use, and most are NOT, then the location of the battery is then a ruling factor.

If you put most AGM batteries under the bonnet, a combination of the charge voltage level and the heat will shorten the batteries life span.

If you have these batteries mounted somewhere other than the engine bay, then there should not be a problem.

If it’s an AGM type then unless it is specifically designed for automotive use, and most are NOT, then the location of the battery is then a ruling factor.

You are referring to SLA's here ("Gel cells", generic non vented black bricks). These need to have the charging rate limited to prevent gassing as they are totally sealed and will explode if charged too quickly.

True AGM's (Starved electrolyte glass mat seperator", Odyssey, Optima, etc) will tolerate any charging at pretty much any rate due to their low internal resistance = low heat generation when charging, and the starved electrolyte system prevents excessive gassing and pressure build up. An alternator charging these directly is OK.

Hi DAMKIA, the problem is that the vast majority of AGMs are not automotive grade and they need to be handled with kid gloves.

Commonly used AGMs like Fullriver and the like, do not tolerate under bonnet conditions and while they will take full inrush currents, they CAN NOT tolerate this form of charging without shortening the batteries life span.

They are also not designed to take the heat of engine bay operations and this again can dramatically shorten their operating life span.

You have to remember, most AGM batteries used in automotive situations were actually designed for use in RAPS ( Remote Area Power Supplies ) and UPS ( Uninterruptible Power Supplies ) where heat and vibration are virtually non considerations.