I have a car and the problem is that it keeps ruining my battery every year or so, i diagnosed everything but failed to decide what is the problem. Even though alternator is not giving above 14.2 but water inside my battery is getting dried.

Voltage while battery sitting idle the whole night : 12.37 Voltage when idle but car running : 14.2 Voltage on all the load : 13.6 Voltage while radiator automatic fan turns on itself and all the accessories are also running : 13.2

Do you think alternator is the problem?

  • Sounds perfectly normal.
    – winny
    Apr 22 '18 at 10:21
  • Check the voltage at higher RPM. Battery can loose "water" over time because of overvoltage.
    – filo
    Apr 22 '18 at 10:26
  • @filo i have rev up the rpms at 2000 and it is more or less 0.1 voltage difference
    – davidweb
    Apr 22 '18 at 10:27

Most Automotive Retail Parts Stores have Charging System Testing machines/tools which will test both the battery and the alternator. These tests are generally offered for free.


Put a small eg. 1W light bulb in series with Battery gnd and if it glows during OFF, you have excessive drain current causing battery premature failures. 50mA max IMO but it could also be 1 or more of 3 phase alternator diode pairs blown

  • Normally, a power drain would not cause the battery to lose water ... can you explain how your answer solves the OP's question? They aren't complaining of power loss or drain. Apr 22 '18 at 14:53
  • If the battery is being drained between uses but not enough to fail starting then the battery charge current will erode the plates faster. Also if the battery is below 12 V for sustained periods which increases plate resistance (Sulphation) which in turn generates heat for the extended charging. This results in excessive electrolyte consumption . Best proof is measure s.g. of each cell. Any weak cell is a total battery failure Apr 22 '18 at 15:11

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