Quote:
Originally Posted by longshot270
Oh oops, I meant the battery charger was reading low, your older post about parasitic draw sounds good to me. I bought the base model XL with no bells or wistles so I was thinking in terms of my truck. But I'm not so sure the extra bells and whistles would draw 80% if your battery in a short amount of time. I've run my truck's stereo plus a pair of 12 inch subwoofers for over 4 hours at full power and only got knocked down to about 9-10 volts. How many CCA (Cold Cranking Amps) is your battery? If I go with my 540 CCA down to 80%, that would be a loss of 108 amps and drop your battery down to something like 10 or 11 volts. Did I mess up on my math somewhere or use wrong numbers? If you left your lights on for a good while I'd expect to see something like that but it sounds like you hook the battery tender fairly soon after parking. I am pretty sure a single 55 watt bulb is usually around 4-5 amps. We must be arguing somewhere but I'm not sure over what. :nerd: 
Question: What is the final voltage after the charger considers the battery to be at 100%? |
We're not arguing at all, Longshot! We're having an adult discussion that often doesn't happen in other forums. But, I suspect we may be referring to different things, so there's a bit of misunderstanding.
Let's go back to my total "parasitic" draw of 0.1 amps. This can drain my Costco battery (I can't give you the CCA on it because it's covered by the battery holder cover in the truck and I don't want to disconnect the battery to read the numbers - but I know it's at least 50 CCA above OEM) in about 21 days.
According to the manual that came with my Battery Tender: A battery that is 100% charged should read about 12.9 V in a "resting", no-load state (which is several hours after being disconnected from any kind of charger). If it is fully
discharged, the resting voltage will be about 11.4 V. If the output voltage is less than 9 V, it is probably defective.
I have another maintainer I use on my trailer batteries called the BatteryMinder Plus, and it says it only goes into the "maintenance/desulphation" mode when the charging voltage reaches 14 V. (It has to get this high during charging, indicating a lot of "back emf" or "charging resistance" to be at a full charge state).
Now, CCA can be a bit misleading. It refers to cranking ability. It's the number of amps a battery can support for 30 seconds at a temperature of 0 degrees F until the battery voltage drops to unusable levels. It's not the same thing as "cranking amps", which is what you get at 32 degrees F and it's not the same as "reserve capacity", which is more a measure of total power stored.
Here's a good link:
http://www.carquest.com/partsBatteryFAQMyths.html#6 It covers many battery facts and myths.
And, back to your point about drain in your post. If I have a 0.1 amp parasitic draw, my Battery Tender, with it's potential 0.2 amp output at an 80%+ charge state is really only delivering 0.1 amps. Pretty puny charging current - but it won't boil the battery, either.
- Jack