To all you 12V specialists out there.
Good afternoon Although this is not strictly RV related, I thought that there was a large amount of 12V battery knowledge here so I am going to give it a shot. I have two dissimilar 12V batteries. ...
Forum Discussion
I don't understand why the bike battery goes dead even with a larger battery in parallel UNLESS the larger battery goes dead too. UNLESS you have a ridiculously long run of small wire to parallel them.
The larger battery should act as a charger for the small one IF the large battery is fully charged to start.
Tell us: What size/type is the larger battery (group 24, 27, 31 etc) and is it an automotive or deep cycle battery?
You have an 8 amp load for 12 hours. That totals 96 amp hours which will KILL any thing except a 200 Amp hour battery, for example a couple of golf carts in series. (A deep cycle lead acid battery should never be drawn below 50% of it's total Amp hour capacity.) A group 27 for instance probably has a capacity of 90 to 100 AH so your load would take that down to fully discharged which will reduce the lifetime of the battery.
I would suspect that with #14 or so wires kept to a reasonable length would do fine as would a 12 A charger on the larger battery. You are taking 8 amps out of the battery leaving an excess of 4 Amps from the charger ONLY WHEN the charger is putting out its maximum. The charger will only put out it's maximum when the battery is partially or fully discharged.
Another thing to keep in mind is that your motorcycle battery is a starting battery and won't last long if you keep drawing it down. Note that 12.2 volts at NO LOAD is a 50% discharged battery. Staring batteries are not designed to do this.
BUT without knowing what batteries you are dealing with every thing is a guess. Please give us what you can on your batteries.
The larger battery should act as a charger for the small one IF the large battery is fully charged to start.
Tell us: What size/type is the larger battery (group 24, 27, 31 etc) and is it an automotive or deep cycle battery?
You have an 8 amp load for 12 hours. That totals 96 amp hours which will KILL any thing except a 200 Amp hour battery, for example a couple of golf carts in series. (A deep cycle lead acid battery should never be drawn below 50% of it's total Amp hour capacity.) A group 27 for instance probably has a capacity of 90 to 100 AH so your load would take that down to fully discharged which will reduce the lifetime of the battery.
I would suspect that with #14 or so wires kept to a reasonable length would do fine as would a 12 A charger on the larger battery. You are taking 8 amps out of the battery leaving an excess of 4 Amps from the charger ONLY WHEN the charger is putting out its maximum. The charger will only put out it's maximum when the battery is partially or fully discharged.
Another thing to keep in mind is that your motorcycle battery is a starting battery and won't last long if you keep drawing it down. Note that 12.2 volts at NO LOAD is a 50% discharged battery. Staring batteries are not designed to do this.
BUT without knowing what batteries you are dealing with every thing is a guess. Please give us what you can on your batteries.
