Stop-start batteries

[pvb]

My 4 year old boat was fitted with Exide Stop/Start AGM batteries as standard for the domestics and bowthruster, and an ordinary Varta AGM for the engine. All working well. The Exides are about £150 for 95Ah and will last for years, so the claim about being "much more expensive" doesn't wash.

 

[pvb]

Yes the agm battery you refer to is ideal for a domestic battery, but it is not a stop start agm battery. The varta stop start range are blue or silver dynamics. Modern cars have a battery management system that is regulated by the car's ECU, the alternator has no built in regulator. Many marine chargers won't charge a stop start agm properly. You can now buy a automotive charger that has an Agm stop start charging mode, if you charge it with an ordinary charger set to gel you will ruin a stop start battery.

Sorry, but that's not good advice. A "stop/start" AGM battery is still an AGM battery. Why wouldn't a marine charger charge it properly? Especially if it were set to AGM, rather than gel?

 

[pvb]

When I asked the question originally about the usefulness of stop start batteries on a boat I wasn't thinking in terms of stop starting the engine but whether the nature of these batteries was such that they might be good (or better) for deep discharge or repeated charging, as commented upon in this post. Or possibly a bow thruster where there could be a number of hard bursts if mooring in difficult conditions.

Yes, they accept charge very readily, which is a good thing. They can also deliver big currents repeatedly, also a good thing. And cycle life is pretty good, as long as you don't discharge them by more than 50%, which is a good rule for most batteries.