Extra Battery for Dry Camping

[rweather]

I have an extra Deep Cycle Battery from my old RV. It is larger than my present batter but is also 12 volts. The manual says that one should only hook up batteries of similar make and type. However I had believed that that there is no problem hooking up two 12 volt batteries with the positive connected to positive and negative to negative. Any thoughts?


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[bdreinv]

Originally Posted by rweather

I have an extra Deep Cycle Battery from my old RV. It is larger than my present batter but is also 12 volts. The manual says that one should only hook up batteries of similar make and type. However I had believed that that there is no problem hooking up two 12 volt batteries with the positive connected to positive and negative to negative. Any thoughts?


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We have two 12 volt batteries in our 16 Eagle, no issues. When they crook will replace with two 6 volt golf car batteries.We have a 275 watt solar system.Living in Arizona don't worry about charging batteries any longer!

[Mustang65]

Sorry, hooking up 2 12VDC batteries with different Ah ratings/sizes is TOTALY not recommended. It would be like hooking up a "AAA" battery in parallel with a "D" battery. The charging and discharging characteristics are different.

If you need 2 batteries, use them separately while camping (discharging) and charging.

Don

My Registry

RVing with SOLAR

[oldmanAZ]

The problem with hooking up unmatched 12v batteries in parallel (positive to positive) is that they usually discharge and recharge unequally. Kind of a 1 + 1 = something less than 2.

If you need to have more 12v capacity, consider switching batteries instead of connecting them together.

How long to you plan to dry camp? Eventually, both batteries will be discharged. How long they will last will depend on how good they are and how much power you pull from them.

[gahris]

From what I have experienced, hooking up two mismatched batteries or the same battery but one is weaker will result in both batteries performing at the level of the weakest one.

[Ela1948]

Originally Posted by Mustang65

Sorry, hooking up 2 12VDC batteries with different Ah ratings/sizes is TOTALY not recommended. It would be like hooking up a "AAA" battery in parallel with a "D" battery. The charging and discharging characteristics are different.

If you need 2 batteries, use them separately while camping (discharging) and charging.

Don

My Registry

RVing with SOLAR

Don, I thru necessity have hooked up 2 group 31's and 2 group 24's in parallel for 3 years now. I have to say they have worked our well. They are all the same age and the same manufacturer. I totally agree that ideally all batteries should be the same size. But I think age and manufacture are really more important then size. At least that's from my experience. Would appreciate your feed back!

[Mustang65]

Originally Posted by Ela1948

Don, I thru necessity have hooked up 2 group 31's and 2 group 24's in parallel for 3 years now. I have to say they have worked our well. They are all the same age and the same manufacturer. I totally agree that ideally all batteries should be the same size. But I think age and manufacture are really more important then size. At least that's from my experience. Would appreciate your feed back!

When you are talking same Age/Mfr/Model/Ah, this makes for an ideal scenario for great performance and long battery life. When you alter one of the items, it will have an effect on the others. Age for example, causes different internal resistances in the batteries. The older batteries need additional charging where the newer batteries do not. When combined the output voltage does not truly represent the actual individual batteries. So, your charge controller is looking at the output voltage of the unbalanced battery bank. The older batteries will be under charged and the newer batteries will be over charged which leads to stratification and an early end to their USEFUL life. While the newer batteries will cause corrosion of the plates, and possibly overheating of the battery.

Different Ah batteries in the same battery bank will be subject to the same above issues.

Granted the Digital Voltage Display will show a nice 13.2VDC, but that may be the output of one battery bank being overcharged and one being undercharged. Also, the rated Ah of your system will be dropping due to the differences of the battery bank. After 3 years you may still be FLOATING at 13.2 volts but your Ah may have dropped from 400 Ah to a current 200Ah, which means a shorter time with full power for dry-camping.

The problem then is that a lot of people just replace the battery(s) that may be causing an issue and the process starts over again.

I already see that in my Trojan T145 batteries that are 5 years old. It takes more Amps being pumped into them to get them topped off by 2-3PM each day, even when they are not being used much.

Don

My Registry

RVing with SOLAR

[Jagiven]

I have two mismatched batteries. I have the oem group 24 dual purpose on the tongue. That's my primary battery. I have a second group 27 true deep cycle battery too. That battery stays at home, if we do not needed it.

I bring the spare along if boondocking. I place it next to the tongue, disconnect the oem battery, and attach a jumper wire I made to extend the wire harness to the spare battery. This method works great for our needs and helps keep the tongue weight down.