Charging AGM Battery

You mean the voltage of the battery in the shops? 12.66V. And probably no less than 12.40 volts (20% discharged) but even then it could be permanently sulfated. General accepted ROT is recharge at 3 monthly intervals (wet cells) or 12 monthly for AGMs. The float voltage depends on the battery type. Refer to batteryfaq-carfaq section 7. The rest of that site should confirm what I have been saying - especially section 9 - though it does not get into the details of paralleling batteries and interconnections etc.

UPDATE... ok purchased batteries from the guy. They are actually used, thats why they were so cheap. I had to meet up with the guy and everything and make sure I wanted them. I checked the voltage of both before I bought them. One of the batteries had just came off the charger @ 2 amp and it was sitting at 13.6v, the other battery he didnt get a chance to charge(why they both weren't charged days ago im not sure) sat at 12.9v. I was good to learn he was selling the batteries just because he was getting out of car audio. Basically to me meaning they weren't burnt out. No I hooked them up just for some test runs, parallel, no isolator or anything. The alternator charges up to 14.1v and didn't drop below 13.4v the entire time I was testing at full tilt around 1500rpm (i was driving). I'm going to charge them fully @ 2 amps before using them anymore. its been 2 hours after the testing and disconnected all the batteries from each other and they are sitting at 13.38v & 13.33v while the shuriken is at 12.78v. Would it be smart to somehow COMPLETELY isolate the shuriken from the other 2 batteries to allow them to last longer, not discharging one another? (I'm going to charge the shuriken fully as well before I put the GPS batteries back in there) And also the the forum is called FloridaSPL.com and they don't even know what I'm doing with my system right now. You are the only person that even knows so far that I have them besides the guy i bought them from lol I dont parade my system around much, i just ask basic OPINIONATED questions on those kind of forums. one of their arguments about me getting to 4000 watts RMS out of ANY amp was with the amp hours. Here's the link to that specific thread. It's basically me just asking what amps work but around page 3-4 they talk about needing 400ah. I looked for more informational threads about it but its basically the same. http://www.floridaspl.com/forums/showthread.php?t=11263&highlight=4000+watt+ampsI can't hear you!

It's a pity they were just charged. You were/are measuring surface charge. They need to sit for up to 48 hours, though often less, for surface charge to dissipate. Or load them with headlights etc for a few minutes. That one of them measures 12.9V after siting for 2 days suggests permanent sulfation - it seems higher than it should be. And yes, IMO you need to isolate batteries from each other when not in use, but you are confusing battery voltages, surface charge and condition. But I won't repeat my isolator solution yet again. You said you tested "at full tilt"? That means with the amp on full? If so, your amp is not outputting anywhere near 4kW. If full tilt means just driving etc, then why would you expect battery voltages to drop or change? They will simply follow the alternator output (except where the alternator drops below the battery voltage). I see no need to charge them (at 2A or anything) - it seems like they are fully charged. But you could, and then I suggest a capacity test. I suspect one of them is below rated capacity. I see the "100ah per 1000 watts" on 4000 Watts RMS amps #42... LOL! I wonder where that rule or quote comes from? Is it a joke, or a misunderstanding? IE - does long420 base it on something, or is he a sheep or an idiot?    I thought you actually had it right, but I see now that you quoted 100ah, not 100A per kW. I took that to be a simple misprint etc - I'm sorry now I didn't pick it up earlier - but I was asking "timing" questions instead. I recall that forum from something else - I think aluminium versus copper (bussbars). Yep - so many fracken idiots that simply miss the point.... PS - If you can, charge the Shuriken; then note its voltage and how fast it drops. You can do that in the car. After a run, kill then engine, disconnect the -ve terminal, then measure the voltage at intervals. It should start from ~13.8V and then maybe drop less than 0.1V per hour. Do a similar comparison with the other batteries (but after whatever charger you use). You could also try running your car on one of the new ones for a while. But carry the Shuriken as a spare!

Yes from my amplifier right now I DO NOT expect 4k watts... why? its only rated 2400 watts AND I didnt have the electrical to power it. I dont think I said anything like that. If you're bringing what I was talking about from the other forum to here then you read that I was going to get TWO of the amplifiers I have now. I'm about to start running this amplifier @ 0.5 ohms (hence why i got the extra batteries as well). They calls for a 200amp external fuse and ACTUALLY stopped producing power with a DMM at 60.2volts AC.Voltage would only go down from there. Honestly I dont know if that matters to you or not, just some fun facts lol "Full Tilt" means the volume of the radio MAXED out and the amps should be maxed out if the gains are set correctly. And when i say 1500RPM's because that is at where i reach at a steady 45-50 MPH on the road that i can turn it ALL THE WAY UP (aka full tilt). and the voltage did not drop below 13.4v. when before it was an easy 11.9v. Come on im not that far behind I know NO load will not drop the voltage. lol Only the shuriken was at 12.9v which is the one battery i've been using this entire time, I want to ISOLATE THAT battery from the RPS batteries. and the shuriken battery has NEVER been charged so I wouldn't doubt the permanent sulfation. I mean i would think it's better to charge all the batteries to full potential before putting them back in the truck. also people talk about batteries that have lower voltage than the other trying to charge themselves on the higher voltage battery? And that's the reason people say to get matching batteries or batteries around the same age for that reason. I am just trying to make these batteries last as long as I can. If the automatic charger is going to make sure they are fully charged for 25$ then why not? I've gotta beat your 1 month prediction lol and I will run that test you suggested ont eh shuriken hopefully today.I can't hear you!

So are you designing for 4kW output or what? I suggested the "12.9V after 2 days" battery you bought is sulfated - not the Shurikan. I suggest you ignore that crap about 100AH per 1000W. It first appears on that site in Jan 2010 but there is nothing about where it is from or what it is based on. (And I could not find it anywhere else.) Until that is known, treat it a bovinepoo - as a misquote of the 100A per 1000W rule. And I'd love to know why they keep recommending more batteries rather than a bigger alternator! (Yes I know "it makes a big difference". Have any of them said an appropriate alternator makes more difference? I can never understand why people recommend bigger batteries when they wouldn't even be used with a bigger alternator! I reckon they're probably idiots that got that batteries first 'cos that was said. They then figured out that just meant a longer to flatten, and the cheapest charger is an alternator anyhow.) I'd be very wary of other advice and products on that site. I love that Crescendo 3K spec - it's another one of those amplifiers with greater than 100% efficiency! (Based on their recommendation for an external 300A fuse since they do not provide a fuse.) But by their own specs, the Crescendo is crap anyhow - how do they vary their output power so much with varying input voltage - an input-proportional SMPS internal rail?    But if you got that Crescendo 3k, you would obviously be getting a bigger alternator and not worrying about the batteries wouldn't you? (Since that will make 2 Volts difference.) But I've done all I can for now. I have accurately predicted what you have found or consistently confirmed it. I have stated what you need for what you were designing. Until you provide answers, there is nothing more I can do. I might hear from you in a month? Else whenever the new (2nd hand) batteries don't meet their reserve time.

lol alright buddy thanks alot it's been nice working with you!I can't hear you!

Just do me a favor and find out WHY they recommend what they do - ie, adding batteries. And ask what "time" they base their 100AH per 1kW rule on. As you said, you had a 220A alternator. Also, if you are measuring 60V AC, you have got BIG problems - unless from an amp (ie, max theoretical 3600W RMS into 1 Ohm?) And a 200A fuse for each amplifier means that they too are NOT 2400W RMS output, but that is already suggested by your tilted non-voltage reduction. And you are no doubt aware that your voltage will reduce with RPM - the alternator profile will handle that. (I think even those FloridaSPL lads recognise the problems with rewired standard alternators - or was that another forum with a wise norseman who rightfully suggested more batteries for SPL comps; he even wrote why NOT to use caps! Not bad for a non-eng soundie.) We also have different opinions as to what work means. Can you hear them laughing too? (Regulars know how I'll get mine... - and got!)

The post-month revisit - refer to rfhvhtoo's relay or isolator page 3 - curious to see if the batteries lasted (if they only need recharging once a month, why bother with them at all?). And still no info regarding this "100AH per 1kW output" rule. I bet it was from an idiot or a battery salesperson!

heyy!! alright look i'm not sure If I told you that I did run a mild .66ohm test with and without the 2 batteries with my old 3 10 inch setup (which is now sold). I'm sure just as we expected you know the amp sounded much better since it has alot more battery power to use with the 2 140's ah as well as the 100ah shuriekn totaling 340 ah... Now The since I was already planning on upgrading speakers and amps, I had a buyer that wanted the speakers asap So i sold those faster than I could buy my next setup. The Batteries havent been used for about 1 month exactly now and they are sitting at 13v. I've charged them once already late december and the initial charged percentage was 98% for both of the RPS while my shuriken was at 67% =/. I bought a 300amp relay that I'm going to be installing when I install my system.... but I did want to ask you. Would it be better for me to have the RPS batteries charging on my alt daily? even though I dont have anything hooked up?I can't hear you!

No.