Seal Lead Acid Battery Question

I resolved my FF battery issue by using two 8AMH batteries connected together to produce 24+ volts.  It works great and appears that the Garmin 400C will run for at least a couple of days with this set-up.  My questions are:  should I keep the batteries connected to a trickle charger or just leave them?  I haven't used the FF for 3 or 4 weeks and the batteries have not been connected to a charger and I just checked them and both are reading nearly 13 volts individually.  If they should be left on a charger; do I need a separate charger for each one?  Would connecting the 12 volt charger to the the combined batteries, charge both?  I know my dual battery setup is unusual and only seems to be required by my Garmin 400C but since I have finally found a battery solution that works, I would like to make sure I'm maintaining the batteries in a way that will maximize their useful life.  Besides that, it's raining and I have nothing better to do than mess with the yak since I can't go fishing.

 

  The batteries will accept charges at different rates, so with this, you can connect both batteries up in parallel, + to +, - to - then the charger to a + and -  on one of the batteries.  Each battery will get something close to an equal charge from your charger, but at half the current one battery would normally get.  If one battery is weaker than the other, the weaker one (Higer internal resistance) will pull a little more charging current.  I think if you connected a 12V charger to 24 volt volt battery you might damage the charger. Haven't done it so I'm not 100% sure. 

I'm confused... does your garmin need 24 volts to operate?  Or just 12?  Just because you are using two 12v batteries, it doesn't mean you are producing 24volts.  It depends if you are wiring them in parallel or series.  That is all beside the point.  You should be fine with trickle charging them at the same time assuming again you have them connected to one another in the 12v arrangement.  Does the charger have an auto off?  I'm not a fan of charging batteries that don't need it... they die faster. 

Maybe you already know this, but just in case... + to +, - to - wiring is parallel and will produce the same voltage as just one battery at a higher AH rate...

+to- connections will give you a series connection doubling voltage, but doing nothing to AH

The batteries are connected in series and yes the Garmin 400C is designed to operate from 12 to 30 volts.  When I used it with one 12 volt 8AMH battery, it only ran for about 4 hours before it began to give error messages and wouldn't function.  I actually returned one to Garmin, thinking it was a defective unit.  After reading the documentation, I discovered the voltage issue.  I was hoping I wouldn't have to disconnect the "series" connections to charge both batteries.  The connection terminals on lead acid batteries appear to be a potential for failure if connected and disconnected often.  I guess I could modify the connections to make them more friendly to being connected and disconnected.  I can always charge each battery separately without disconnecting them.  I was just looking for something a little more simple like a connection from the charger with the same plug as I use to connect to the FF. 

The batteries are connected in series and yes the Garmin 400C is designed to operate from 12 to 30 volts.  When I used it with one 12 volt 8AMH battery, it only ran for about 4 hours before it began to give error messages and wouldn't function.  I actually returned one to Garmin, thinking it was a defective unit.  After reading the documentation, I discovered the voltage issue.  I was hoping I wouldn't have to disconnect the "series" connections to charge both batteries.  The connection terminals on lead acid batteries appear to be a potential for failure if connected and disconnected often.  I guess I could modify the connections to make them more friendly to being connected and disconnected.  I can always charge each battery separately without disconnecting them.  I was just looking for something a little more simple like a connection from the charger with the same plug as I use to connect to the FF. 

Thanks for clarifying.  Have you tried to operate the garmin with them in parallel?  That should give you better life than just the one battery and would make charging them easier.  By the way, I don't know for sure that you can't charge a 24v system with a 12v charger, it is just that I a charger with a switch on it for 24v, and I figure if there was no difference the switch wouldn't be there. 

It's too bad that thing is such a battery hog... look like a great unit.  I have a lowly lowrance x50ds but it will run for days on just one SLA battery.

Thanks for the info.  I just checked my charger and it has a switch for 6 or 12 volts.  I think it's a pretty good assumption that charging the 24 volt combo with a 12 volt charger is not a good idea.  I think I'll look into getting a 24 volt charger.

you will burn your charger up if you try to do 24 volt with a 12 volt charger. I would use plugs wired to make them in series then change to parallel. by just plugging in the proper plug for what you want to do. That way you will have the best of both worlds. but avoid the hassle and series will give you twice the power in time to run.