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I have been experiencing a slow draining of the battery for the past 1-2 months wherein the vehicle will be fine and suddenly the vehicle will not start.

First thought was the battery, as the vehicle has about 90000 on it. I could have tested it, but didn't; just bought another one thinking it would save the trouble soon enough if it wasn't the battery. On installing the battery, I checked for the usual: lights left on, doors left open, etc. But there was nothing out of the ordinary.

Two weeks later, the new battery drained. I charged up the old one swapped it in. One week later, that one was drained.

Determined now that it was not the battery, I searched high and low for some good tests. I did a ground test (all less than 2-1ohm), point to point resistance check(all 1-2ohm), parasitic draw test (30mA after entering sleep mode), and charging voltage test. Everything looked satisfactory. The only thing that I noticed was, if I left the nominal voltage charging test run, for minutes, I would slowly watch the voltage creep down. After twenty minutes I was seeing 13.8V after starting at 14.3V (measured across the battery terminals). I ran out of time to swap out the battery on my multimeter (thinking this might be the culprit), so it could just be that. But, I'm curious. Does a slow fall of the charging voltage (across the battery terminals) indicate an alternator problem? Belt tensioner problem? Looking for thoughts on this slow decline in charging voltage across the battery to determine where to dig into next. I didn't see how low it could go, but if the community thinks it's worth a shot, I'll do it (even if it means an hour to find it).

The vehicle: '08 Nissan Rogue, AWD. 90k miles.

The problem has reoccurred once in the past month (10/15), after charging up the battery, I took it to Auto Zone for an alternator check where they informed me that everything was ok. I'm starting to wonder about belt tensioner. Perhaps the belt is slipping past the alternator and the charging voltage is dropping.

  • Which vehicle is this (make, model, year)? – Zaid Jun 8 '15 at 11:58
  • Added make model Zaid – N8sBug Jun 8 '15 at 12:01
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I would place this as being an issue with the alternator. Take it in and have it checked, but I bet the reason is one (or more) of the diodes in the alternator is not working, which does not allow for a charge to occur correctly. Any of the major parts chains (AutoZone, Advance Auto, O'Reilly's, etc.) can and will check it for you for free. This seems like normal behavior for an alternator with issues.

  • Could you specify which behavior indicates an alternator issue? 13.8 V seems like a normal voltage range for a battery that is being charged. – Zaid Jun 8 '15 at 12:43
  • The fact that the voltage continues to drop over a period of time as you are running the engine. This is indicative of poor alternator performance. – Pᴀᴜʟsᴛᴇʀ2 Jun 8 '15 at 12:44
  • siding with Zaid, i thought 13.8 while charging was a good way to know alternator is working till today .. @paulster you mean to say that even though the alternator charges the battery it can be broken? – Shobin P Jun 8 '15 at 13:27
  • @Anarach - It may be charging at a reduced rate. I'm suggesting this is a good place to start and the most plausible problem with the charging system, especially if you are starting from a fully charged battery. – Pᴀᴜʟsᴛᴇʀ2 Jun 8 '15 at 13:29
  • I also feel what paulster2 says is correct. It could be the regulator that is part of alternator that is culprit. If the regulation voltage of alternator is checked at no load and full load and the charging current is tested, this can be confirmed – knocksAndMisfires Jun 8 '15 at 15:14

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