609albert Posted October 23 Share Posted October 23 My buddies 50 Mack LS 85 fire pumper ,everything was ok then truck needed to be jumped to start , park truck , no battery to start jump again , has 2 12 volt batteries, where to trouble shoot first ,batteries are newer. is it the voltage regulator ,generator/alternator ,rectifier , all wiring looks good .don't know if ammeter is good yet Quote Link to comment https://www.bigmacktrucks.com/topic/74674-batteries-not-holding-charge/ Share on other sites More sharing options...
skydawg Posted October 24 Share Posted October 24 I`d put a test light between a battery post and cable to see if there`s a current draw when parked. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/74674-batteries-not-holding-charge/#findComment-560661 Share on other sites More sharing options...
mechohaulic Posted October 24 Share Posted October 24 being a fire pumper, should have a dual start system ; does it have the master disconnect switch ?? having "start 1 /start 2 ??seems some what a light battery program ' meaning only 2 -- 12's , not 2 sets of 6 ? any electrical work done lately on a possible positive ground unit and someone hooked a negative ground device ?? Quote Link to comment https://www.bigmacktrucks.com/topic/74674-batteries-not-holding-charge/#findComment-560665 Share on other sites More sharing options...
JoeH Posted October 24 Share Posted October 24 Voltmeter across the terminals while off, what's your voltage? When running what's your voltage? Should have 12v off, and 14v while engine is running. Each battery has 6 caps you can remove to check water level and if you have a battery float tester you can check the charge under each cap. One bad cell will draw down all the batteries. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/74674-batteries-not-holding-charge/#findComment-560666 Share on other sites More sharing options...
Brocky Posted October 24 Share Posted October 24 (edited) How long did it run before shutting down again?? How long does it sit??? A battery tender / minder is cheap and might solve the problem???? check their specs, you might need either a heavier one for both 12V batterys?? or one for each??? Edited October 24 by Brocky 1 Quote Brocky Link to comment https://www.bigmacktrucks.com/topic/74674-batteries-not-holding-charge/#findComment-560669 Share on other sites More sharing options...
h67st Posted October 24 Share Posted October 24 If you do have a draw on the batteries, the regulator is the most common cause of that. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/74674-batteries-not-holding-charge/#findComment-560686 Share on other sites More sharing options...
Freightrain Posted October 24 Share Posted October 24 53 minutes ago, h67st said: If you do have a draw on the batteries, the regulator is the most common cause of that. Points are stuck. Crazy thing on my old Cub cadet since starter is also generator. If the points stick on regulator, if you turn it off the it will sit and crank itself if(been there). Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/74674-batteries-not-holding-charge/#findComment-560692 Share on other sites More sharing options...
609albert Posted October 26 Author Share Posted October 26 he is still checking all suggestions out with truck Quote Link to comment https://www.bigmacktrucks.com/topic/74674-batteries-not-holding-charge/#findComment-560865 Share on other sites More sharing options...
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