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I was told to charge the battery every so often to keep the battery life at a high, does this damage the alternator by constantly charging the battery from a home charging system?

  • Welcome to the site. Glad you could join us. What do you mean by charge the battery? Using an external charger? Or using the alternator to charge the battery? – Pᴀᴜʟsᴛᴇʀ2 Mar 5 '17 at 15:34
  • pointless, but it wont hurt anything – agentp Mar 6 '17 at 3:43
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No, charging the battery from home should not damage the alternator. There is however no need to constantly charge it. If the vehicle is being used frequently there's no need to keep charging it at all really as the alternator will keep the battery charged up just fine.

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A full discharge and recharge is beneficial to certain types of battery (e.g. laptops) but not to the lead-acid batteries in cars. Lead-acid batteries are happiest when they have a constant current trickling through them - a regularly-used vehicle may never need its battery replacing, my Ford Fiesta had its original battery from 1999 when it was written off in 2012. Deep-discharging kills lead-acid batteries, and you may find if your battery runs flat, it won't hold as much charge, and begins to slowly degrade past this point. A maintenance cycle on a smart battery charger can bring it back almost as good as it was. This may be in line with the advice you were given.

Alternators used to be primitive devices, but now have sophisticated voltage regulators and control circuits that prevent many of the classic scenarios that older mechanics may have told you about (I remember advice my grandfather gave me about 20 years ago, which has become obsolete). That's not to say they can't burn out if they're overloaded, and charging a dead battery can draw quite a lot of amps, but the scenario is very unlikely and would probably require the alternator to be failing anyway. In realistic terms, the alternator itself is constantly charging the battery (except on certain newer vehicles where the alternator shuts off to save fuel), so there is no harm in it.

  • Actually, automotive lead acid batteries benefit from complete discharge with moderate current and immediate recharge once per year. – Paul Mar 19 '17 at 18:36
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The alternator isn't designed to recharge a dead battery. It's intended to maintain the charge on a good battery. When this does happen, the alternator begins to run hot, and this is what kills the alternator.

  • Can you provide evidence to back up your statements? If I was an alternator manufacturer, I would put a current limitation to the alternator that would keep it operating within its specs. I presume that's what the alternator manufacturers do. Besides, if the battery is dead (as in won't accept charge), no amount of charging is going to save it, and the current should be so small that it eliminates the theoretical possibility that the alternator will overheat. – juhist Mar 7 '17 at 15:03
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using alternator to charge dead battery can damage the alternator, using home system can not damage the alternator.

  • Welcome to mechanics SE! We're glad to see you here. Would you mind expanding this answer a bit? How does charging the dead battery damage the alternator, and why? Including references would also be good. – anonymous2 Mar 6 '17 at 19:45
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    The alternator isn't designed to recharge a dead battery. It's intended to maintain the charge on a good battery. When this does happen, the alternator begins to run hot, and this is what kills the alternator. – Sopuru Ofoegbu Mar 6 '17 at 20:45
  • @SopuruOfoegbu A substantial percentage of vehicles on the road still use shunt-based alternators, which run at 100% output all of the time. – Paul Mar 19 '17 at 18:34

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