Hi all! first post here and I just had a (possible) basic question.I am putting a double battery setup on my new 18' trailer.2 Interstate 31m-agm's.the reserve capacity of this battery is 190I have never run batteries in a parallel so my question is two folddoes that mean I will have exactly double the reserve capacity?so aprox 6 hours draw at 25amps?and if I were using a small tv that pulled 2amps.what would be my aprox run time before I needed to stop running the TV and recharge the battery?I just don't know how to calculate thisalso, if you think these batteries are not what I should be getting, I am open to hear why.Thank you!

Take how many amp hours you have and double it for two batteries. Then never let it go below 50% charge.I have 430 ah which would power a 2 amp tv forever with my solar recharging it.

Solar is an easy and quiet way to recharge RV batteries...which should be fully recharged daily for maximum life.

macscac wrote:2 Interstate 31m-agm's.They aren't what you should be getting. From what I see those appear to be engine starting batteries.

The battery is rated at 100Ah which is the rating you want to use for house batteries. So 200Ah total in parallel. Best to limit the drain to 50% or 100Ah.You didn't specify 2A AC or DC for the TV. Assuming AC then the inverter would draw 20A+ and your run time is 100Ah/20A = 5 hr. If DC then it's 50 hr. That's for a 100% charged battery.However RVs have other drains like refer, smoke detector, lights etc. Plus I would not use a battery rated for both starting and house. Instead I'd use 2 6V deep cycle batteries in series. Typically they are about 220Ah but designed for more cycling.

Well Mac, The golf cart batteries are the hot set up... They are designed to survive that sort of abuse. They are typically in the range of 220+/- ampere hour and can be depleted to 50% without damage. Lifeline AGM say that they can do this 80 cycles with no loss of capacity. What you are trying to figure out is the rating given because car battery manufactures did not want to be held to a 20 hour rate for Ampere-Hour capacity. What reserve means (kind of) is "How long can I leave the headlights (~25amp) and still start an engine" that doesn't need a lot of cranking (because it won't be there). That measure goes from 12.8V starting at 25amps until the terminal gets to 10.5V (iirc). At 10.5 most Lead Acid batteries have been harmed. You get to do this about three times before that jar is toast.Go with the golf cart pair in series. Matt

Parallel batteries and a question regarding reserve capacity

18 Replies

allen8106
Explorer
Jun 11, 2019
macscac wrote:
Thank you all for the quick responses..

Matt_colie, what battery specifically would you recommend?

Crown batteries are my recommendation.
valhalla360
Navigator
Jun 11, 2019
Actually paralleling two batteries will gain you more than double. The higher ratio of amp draw relative to the amp-hr rating, the less amp-hr are actually available...by doubling the batteries, you cut that ratio. Don't expect a huge improvement but a little.

6V golf cart batteries are popular because it's hard to find true deep cycle 12v batteries and they often come at a premium price. 200-300amps out of golf cart isn't going to harm it.
time2roll
Nomad
Jun 11, 2019
If you want AGM I recommend Lifeline brand deep cycle.
For best value the Costco/Sam's Club GC2 will serve you well.

Next to review is your charging system. Many converters like WFCO are known for chronically undercharging batteries and providing a slow charge when running a generator.
Dusty_R
Explorer
Jun 11, 2019
Check your TV. Many of them plug into 120v receptacle but have a wall wart and the tv is 12v dc.
wa8yxm
Explorer III
Jun 11, 2019
Forget "Reserve capacity" that only applies to starting

Two Group 31's about 130 amp hours each means you have 260 amp hours of which you can use about 25%. unless they are full DEEP CYCLE (in which case Reserve Capacity likely won't be specified) in which case you can use 50%. so you have about 75 amp hours of safely usable power before you damage the batteries.

Now with a pair of GC-2 Flooded wet cells you'd have 220 total amp hours and 110 usable (50%) since they are true DEEP CYCLE
Crabbypatty
Explorer
Jun 11, 2019
Trojan T 125s 2 6 volt GC batteries. Sold my first TT with them on after 10 years going strong. Bought our second TT now 5 years, selling that. Upgraded to a Fifth Wheel, added two more for 4-T125's As mentioned never let them go below 50% and they will last forever.

Present set up, as we dry camp a lot. 428 watts solar, 4 t125s, 2000 watt Xantrax inverter. Led lights through out. Turned off converter, frig and water heater to gas, plugged in inverter and fiver is powered up. Adding a few more solar panels. Only issues are long dark days. We also carry a honda 2000 for back up. Hope this helps.
pianotuna
Nomad III
Jun 11, 2019
Hi,

2000 watts is definitely in the large category, at up to 200 amps of demand (@ 12 volts). My own is 3000 watts and I've been known to draw 290 amps from the battery bank.

macscac wrote:
pianotuna wrote:
There are those of us who use large inverters and load them heavily. In that instance 12 volt jars may offer better service than 6 volt units.

It is important to wire any battery bank in a balanced manner. See the link for directions.

Reserve capacity, just like the more familiar amp-hours may more than double because of the Peukert effect.

***Link Removed***

what is defined as a large inverter?
i allready have one small inverter but it runs the heater and lights. none of the 110 outlets work from it so I will be installing a second one to run an outlet to charge devices and a tv. thats pretty much it.
I was looking at a 2000 inverter from amazon.
2oldman
Explorer II
Jun 11, 2019
macscac wrote:

i allready have one small inverter but it runs the heater and lights.
heater and lights are 12v
macscac
Explorer
Jun 11, 2019
pianotuna wrote:
There are those of us who use large inverters and load them heavily. In that instance 12 volt jars may offer better service than 6 volt units.

It is important to wire any battery bank in a balanced manner. See the link for directions.

Reserve capacity, just like the more familiar amp-hours may more than double because of the Peukert effect.

***Link Removed***

what is defined as a large inverter?
i allready have one small inverter but it runs the heater and lights. none of the 110 outlets work from it so I will be installing a second one to run an outlet to charge devices and a tv. thats pretty much it.
I was looking at a 2000 inverter from amazon. i (obviously) dont know much about this sort of thing so I am just trying to fumble thru it

https://www.amazon.com/dp/B00T93K9KU/?coliid=I1PVOH544B4GC1&colid=HC41G32TCGVK&psc=0&ref_=lv_ov_lig_dp_it
MEXICOWANDERER
Explorer
Jun 11, 2019
My vote is for the 31 Lifeline in parallel.

AGM batteries always render higher CCA qualities than standard flooded of the same group size.

Add that to the fact that the Lifeline has the highest rating for 100 hour discharge and the plates are twice as thick and it adds up to an almost no brainer.

Whom else makes their battery from case to lead paste in the USA? Deka will not respond to me to the answer. Even the lowly spiral batteries now come from Mexico.

Read the online LIFELINE USER MANUAL and obey it.

Charging is simple. 2 group 29 Lifelines XT batteries hold 100 USABLE amp hours. A simple Megawatt charger adjusted to 14.4 volts with a tiny screwdriver can recharge them "good enough" in four hours to endure a 3 month trip without a total charge. To total charge, get to an overnight power plug then plug the battery in at night and disconnect it in the morning. Can't get any simpler than that.