Upgrading from group 27 to golf carts

JamesJudasPriest wrote:
In my imagination, the batteries charging over night before the trip, driving with a powerful alternator, and having a small top up at the campsite for a few days was going to be enough.

Given a few days I would upgrade to the GC's, try it and determine what else you might need to change.

There are posts on multiple day camping on 2 GC's.

Thanks for all the replies. I realize I should not go below 50% SOC, hence why I am wanting to upgrade my small battery that is getting over worked and heavily depleted. Don't worry Roy, I don't have a diode isolator for that exact reason on the voltage drop. Maybe I wasn't clear on the charging voltage... Say I stop draining the batts at 50% SOC, then I use the generator. I was hoping to set the charge wizard to 13.2 volts for a few hours to keep the current at around 20A. Then, after that set it to 13.6 for 2 hours, still around 20A and hopefully even at 14.4 volts it will still not go over 20A. Maybe I'm dreaming. I do know the importance of having full 14.4 charge voltage, what I am hoping to get away with is having a constant current method of charging... 2 hours at 13.2, another 2 at 13.6 and then setting it at 14.4. After this, hopefully leaving the converter to decide the best voltage.

Thanks guys. Maybe I do have to bite the bullet and get bigger generator. In my imagination, the batteries charging over night before the trip, driving with a powerful alternator, and having a small top up at the campsite for a few days was going to be enough.

Unfortunately, without the aid of a solar charging system, a 350w generator isn't going to do much for a multi-battery pack. Any way you look at it, you need to invest some money to get where you want to be.

Charging deep cycle batteries follows a scientific rule of which there is no short cuts..

Consider this charging report from Progressive Dynamics on how long it takes to re-charge a deep cycle battery using different DC charging voltages.

"Progressive Dynamics ran this test on the amount of time it took a PD9155 (55-amp) converter/charger set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts.

14.4-VOLTS (Boost Mode) – Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.

13.6-VOLTS (Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.

13.2-VOLTS (Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge."

There is also a rule of thumb of each deep cycle battery will demand around 15-20AMPS of DC current at the 14.4VDC level. Most of us use the 20AMP DC current level.

For your two 6VDC batteries you will want to have at least a 45 AMP smart mode Converter/charger to use like the PD4645 or PD9245 converter. Just charging your GC2 batteries for a couple of hours at DC Voltages less than 14.4VDC will not come anywhere close to 90% state of charge meaning your batteries will drop like a rock when you try to use them again.. This will eventually damage your batteries.

I would convert to 4AWG cables everywhere in the battery charge system from the converter/charger to the battery bank.

You was asking about the size of the GC2 batteries. This is a TROJAN T105 GC2 battery spec sheet


The GC2 Batteries are considered a Group 24 battery but are taller than the standard GP24 battery..

You can compare the T105 battery specs to this Trojan typical GP27 12VDC Battery for size comparison.


The PD4645 and PD9245 will require 550-725 WATTS AC INPUT power to operate them. This will require at least a 1KW Honda type Generator to provide that much power. The 1KW Honda generator should produce around 900WATTS rated AC output power.

Regarding using the Alternator for charging additional batteries i would only entertain a SMART MODE SOLENOID that would monitor your added battery bank and switch into your alternator charging system when the DC level has dropped to a settable point. This would add your battery bank in parallel with your truck starting battery when this happens. When they charge back up it would then switch out. Since your motor must be running to activate this method of charge this method would never discharge your truck start battery by running down the added battery bank. A SOLENOID must be used with deep cycle batteries verses the older DIODE BASED ISOLATORS as the diode isolator has a large .7VDC voltage drop across the diode. In this case if your alternator was trying to use 14.2VDC in boost charge mode it would actually only be 13.5VDC due to the voltage drop across the high current diodes so getting a quick three hour charge is now going take around 12 hours of time to charge back to the 90% state of charge.

Lots of things to consider here it seems...

I am thinking you are not going to be happy with your described system for recharging your GC2 batteries.

You are also going to need a larger generator...

I'm sure others on here will have different ideas for you. This is my take of the issues primarily based on my previous 5-6 years of running my 255AH 12VDC Battery bank off the power grid..

Roy Ken

A 350 watt genny is not going to be able to power anything but a very small battery charger - 15~20 amps max and that's with no other loads.

At 10% SOC you will likely need a new battery. Don't deplete house batteries below 50% SOC. You really need to read this: http://www.marxrv.com/12volt/12volt.htm

10% SOC is extremely low. Definitely not recommended to go that low. The GCs can take 50A in bulk so 19A will take awhile.

If you're not going to get a bigger gen then I'd try the 75A alternator first. You'll have engine power usage but no vehicle lights etc so it might be OK when idling. A DC clampon ammeter would help to make better decisions. About $50.