Charging Batteries

[Bob P.]

Hi all. I have a 2024 hd2500 gasser with a factory auxillary battery and wondering if trickle charger on main battery will also be maintaining aux. battery also or have to charge it seperately. Thanks.

[Another JR]

I believe that, once the main battery is charged enough, the charging voltage will be sufficient to close the isolator and charge the second battery.   It should be easy to verify this with a voltmeter. 

[4th Duramax]

No need to charge separately. Charge the drivers side one that is easy access. If I remember right, one of my older owners manuals said never to jump another vehicle using the passenger side battery so I never mess with that one. Besides that it’s a pain to get to.

[Another JR]

2 hours ago, 4th Duramax said:

No need to charge separately. Charge the drivers side one that is easy access. If I remember right, one of my older owners manuals said never to jump another vehicle using the passenger side battery so I never mess with that one. Besides that it’s a pain to get to.

The OP has a gas truck, which has a battery isolator. The diesel trucks have parallel start batteries with no isolator. Based on your user name I’m thinking your truck may be a diesel. The question for the OP is whether his trickle charger will close the isolator. The answer will depend on how the isolator functions. A voltage sensing isolator likely will close once the main battery charging voltage gets high enough. An ignition signal driven isolator won’t close unless the engine is running or you fool it somehow.  I don’t know which type of isolator is installed, but a voltmeter will tell you when the isolator is closed. 

[Chopper_Man]

Even with an isolator, how would you prevent the main battery from overcharging?

 

Chargers leads on main battery > Main battery charged > isolator closes allowing to charge 2nd battery > main battery still on the charger thus the potential to over charge.

 

While it's rare I need to, but on dual batteries I have always charged using 2 chargers with the 2nd batteries ground disconnected.

[Wxman]

With the factory GAS setup the two batteries are only connected with ignition in 'run' position.  This allows charging of aux battery by alternator.  In other ignition positions the two batteries are isolated.  This protects starting battery from discharge when using aux battery for camper, accessories etc.

With ignition off, charging either battery alone will not charge the other battery.

I use a two bank NOCO Genius during extended garage times.

Cheers