Would it be wise to attach another battery to the electrical system?
Thread Starter
Lexus Test Driver
Joined: Feb 2001
Posts: 1,185
Likes: 6
From: California
There are benefits and drawbacks to doing this.
Benefits are extended usage with the key off, and also the ability to use the stereo until the battery is dead, then still be able to start the car.
The drawbacks are that you will need to engineer this correctly, or you will be in for more trouble than it's worth.
1. Be sure your alternator can handle the increased amperage load. Do be aware that once a car is started, all of the electronics are running off of the alternator, NOT the battery(ies). At that point, the battery(ies) are simply an additional load on the alternator, which is actually a worse situation than if you had only one battery.
2. Be sure you have the batteries isolated when the engine is not running. If you simply hook the batteries in parallel, they will both drain together, which will double your usage, but also kill the starting battery (which was the whole reason for putting the second battery in the first place!) While draining both is only inconvenient, there is a VERY serious additional problem which is addressed in #3 below...
3. If you don't have identical batteries, of the same brand, size and age, each will have a different resistive load. This will causes an imbalanced charge to go to the batteries, which will in time overcharge one of the batteries. At that point it will start boiling over and heating up until it is completely dead. In the meantime it will vent, bubble, etc. and spew acid crap everywhere.
4. Even if you did have identical batteries, they will need to be wired with the exactly same size AND length of wire from the charging source, or you will once again introduce a different resistive load which will once again cause this severe charging imbalance problem. Also note that if one is more drained than the other, it will start to suck power from the other battery as soon as they are connected together.
5. Battery isolators are ok, but these are basically very large diodes which introduce a significant power drop through them, which will be in excess of 1-1.5 volts. Once again, you are defeating the purpose of having extra batteries if you drop the useable voltage like this.
6. An isolator relay does a good job because of no drop in voltage, but you had better be aware of the points above with different batteries, different levels of discharge, different cables and cable lengths, etc.
Basically, it comes down to: Are you doing this for extended use of the stereo when the car is not running?
If the answer is yes, then do upgrade to better or additional batteries. I would strongly suggest going with an Optima Yellow over anything else.
If you do put the extra battery(ies) also upgrade the charging system, as you will put undue strain on the factory alternator, which is barely adequate to begin with.
If you are not going for extended use with the engine off, your best bet is to upgrade the alternator only. While this is expensive, it is the most worthwhile thing you can do.
Todd M.
TM Engineering
http://www.tmengineering.net
Benefits are extended usage with the key off, and also the ability to use the stereo until the battery is dead, then still be able to start the car.
The drawbacks are that you will need to engineer this correctly, or you will be in for more trouble than it's worth.
1. Be sure your alternator can handle the increased amperage load. Do be aware that once a car is started, all of the electronics are running off of the alternator, NOT the battery(ies). At that point, the battery(ies) are simply an additional load on the alternator, which is actually a worse situation than if you had only one battery.
2. Be sure you have the batteries isolated when the engine is not running. If you simply hook the batteries in parallel, they will both drain together, which will double your usage, but also kill the starting battery (which was the whole reason for putting the second battery in the first place!) While draining both is only inconvenient, there is a VERY serious additional problem which is addressed in #3 below...
3. If you don't have identical batteries, of the same brand, size and age, each will have a different resistive load. This will causes an imbalanced charge to go to the batteries, which will in time overcharge one of the batteries. At that point it will start boiling over and heating up until it is completely dead. In the meantime it will vent, bubble, etc. and spew acid crap everywhere.
4. Even if you did have identical batteries, they will need to be wired with the exactly same size AND length of wire from the charging source, or you will once again introduce a different resistive load which will once again cause this severe charging imbalance problem. Also note that if one is more drained than the other, it will start to suck power from the other battery as soon as they are connected together.
5. Battery isolators are ok, but these are basically very large diodes which introduce a significant power drop through them, which will be in excess of 1-1.5 volts. Once again, you are defeating the purpose of having extra batteries if you drop the useable voltage like this.
6. An isolator relay does a good job because of no drop in voltage, but you had better be aware of the points above with different batteries, different levels of discharge, different cables and cable lengths, etc.
Basically, it comes down to: Are you doing this for extended use of the stereo when the car is not running?
If the answer is yes, then do upgrade to better or additional batteries. I would strongly suggest going with an Optima Yellow over anything else.
If you do put the extra battery(ies) also upgrade the charging system, as you will put undue strain on the factory alternator, which is barely adequate to begin with.
If you are not going for extended use with the engine off, your best bet is to upgrade the alternator only. While this is expensive, it is the most worthwhile thing you can do.
Todd M.
TM Engineering
http://www.tmengineering.net
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