Battery keeps dying

woody367

TJ Enthusiast
Joined
Nov 6, 2017
Messages
248
Location
Long Island, NY, United States
SO MY tj has been sitting and went to start it and nothing. Jumped it and ran it for awhile and all good. A week later dead. I use to sit for months and would start right up. Only thing that has changed was I put the factory rear wiper setup in. Will that have a draw even when Jeep is off?
 
Check the condition of the battery cable clamps, terminals, and cables for corrosion and tightness.
After jumping starting the Jeep you need to check the charging voltage and after a long drive check the battery voltage while idling; then after you shut off the Jeep you need to monitor the resting battery voltage and observe where the battery voltage settles at.
IF the voltage settles around 12.5V after a couple hours; then restart the Jeep and observe where the voltage drops to while cranking over the engine.
IF the voltage drops below below 12V while cranking the engine or IF the voltage after a couple resting hours drops to below 12.2V; then the battery either has a bad cell or there is a large parasitic draw on the battery from an accessory or ground.
You can test for amp draw by removing the ground cable clamp from the battery, placing a VOM leads between the battery terminal and cable clamp, place the VOM mode selector on mA and measure the Draw.
IIRC the amp draw from the radio and ECU shouldn't be much more than 35 mA.
 
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Check the condition of the battery cable clamps, terminals, and cables for corrosion and tightness.
After jumping starting the Jeep you need to check the charging voltage and after a long drive check the battery voltage while idling; then after you shut off the Jeep you need to monitor the resting battery voltage and observe where the battery voltage settles at.
IF the voltage settles around 12.5V after a couple hours; then restart the Jeep and observe where the voltage drops to while cranking over the engine.
IF the voltage drops below below 12V while cranking the engine or IF the voltage after a couple resting hours drops to below 12.2V; then the battery either has a bad cell or there is a large parasitic draw on the battery from an accessory or ground.
You can test for amp draw by removing the ground cable clamp from the battery, placing a VOM leads between the battery terminal and cable clamp, place the VOM mode selector on mA and measure the Draw.
IIRC the amp draw from the radio and ECU shouldn't be much more than 35 mA.

Just make sure to leave the ignition switch to off, otherwise you'll make the fuse in your meter gay.
 
Once a battery is allowed to go dead and the engine is then jump-started, the battery won't fully recharge with just short driving trips. The alternator was not designed to recharge a dead battery and won't unless driven a very long distance without stopping. Place it on a good benchtop battery charger, not a trickle charger, OVERNIGHT and let it get fully charged. A couple hours on a battery charger won't do it.

And know too that the more a battery is allowed to be fully discharged, the less charge it can hold and the more easily it can be drained dead again. They don't recover fully after going completely dead.
 
I've seen shorted rear wiper motors drain battery's on other SUVs, not sure if a jeep tj has the same wiring to allow it to happen but couldn't hurt to disconnect it after you're sure about the battery state
 
So I tested the battery and it is done, I am going to replace it but was wondering what is the biggest CCA and ah battery i should get. I do plowing with the TJ in the winter. Stock calls for a group 34 but was told get a 31 for more ah. I want a lead-acid not AGM. Once replaced I will check the whole system. Thank
 
Why would you want a conventional "wet cell" battery when AGM batteries are more powerful for their size and far more rugged & longer lasting? A good Group 34 AGM battery would be a good choice for your snow plowing.
 
Battery over three years these days is suspect. Regular flooded lead acid fully discharged once is toast. Sorry but if the battery was dead it is dead.
 
Nothing wrong with our charging system and AGM. The small differences in voltage are far outweighed by the advantages of AGM. Honestly, charging to 100% is almost universally considered terrible for battery life so I'd say our systems are just fine.
 
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Nothing wrong with our charging system and AGM. The small differences in voltage are far outweighed by the advantages of AGM. Honestly, charging to 100% is almost universally considered terrible for battery life so I'd say our systems are just fine.
I've been running nothing but AGM batteries in my TJs for over 20 years, the TJ's OE charging system works fine with them and so does my old bench top battery charger that does not have an AGM mode. Discharging to 100% dead is bad for our batteries but charging them to 100% fully charged is fine.
 
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