I've had a yellowtop in parallel with my front battery for over 2 years now across 2 vehicles and not had problems with it draining the front battery.
The yellowtop resting voltage is identical to the lead acid's resting voltage up front - 12.6volts.
2 circuits in parallel with identical voltages will not transfer any current between eachother. This is a law of electricity. Unless something is causing one battery to have a lower voltage (damage or a steady draw on it), it's not going to pull OR push current to the other battery in any sizable amount.
If you put a HEAVY HEAVY load on the circuit and one battery has a considerably different internal resistance than the other (read: is ****ed up, or WAY smaller than the other in capacity and output ability), one battery could get flogged harder than the other, causing it's voltage to drop below recommended levels (not a problem for the yellow top) while the overall system see's a 'healthy' voltage -- but you're talking MASSIVE amperage in that case, and you could easily measure this difference with a cheap DVM - and you should know what you're doing before playing with that kind of current.
An isolator is only needed if you intend to play your music for extended periods of time and/or at loud volumes without the engine running. This is to keep your front battery from dying when you drain your gel cell. This IS important in stuff like RV's where you have a battery for your appliances in the back and you tend to drain the ****er alot, but in a car (Daily driver) you won't ever see that yellowtop drain to the point where it would kill the front battery. In fact, you may find that having a yellowtop in the back in parallel actually shields you from the signs of a failing front battery somewhat.
The yellowtop resting voltage is identical to the lead acid's resting voltage up front - 12.6volts.
2 circuits in parallel with identical voltages will not transfer any current between eachother. This is a law of electricity. Unless something is causing one battery to have a lower voltage (damage or a steady draw on it), it's not going to pull OR push current to the other battery in any sizable amount.
If you put a HEAVY HEAVY load on the circuit and one battery has a considerably different internal resistance than the other (read: is ****ed up, or WAY smaller than the other in capacity and output ability), one battery could get flogged harder than the other, causing it's voltage to drop below recommended levels (not a problem for the yellow top) while the overall system see's a 'healthy' voltage -- but you're talking MASSIVE amperage in that case, and you could easily measure this difference with a cheap DVM - and you should know what you're doing before playing with that kind of current.
An isolator is only needed if you intend to play your music for extended periods of time and/or at loud volumes without the engine running. This is to keep your front battery from dying when you drain your gel cell. This IS important in stuff like RV's where you have a battery for your appliances in the back and you tend to drain the ****er alot, but in a car (Daily driver) you won't ever see that yellowtop drain to the point where it would kill the front battery. In fact, you may find that having a yellowtop in the back in parallel actually shields you from the signs of a failing front battery somewhat.
