sony head unit discharging battery

Well oldspark, you seem to know your stuff as this is exactly what I have been learning with this AGM battery of mine. It's not an optima, but it is an AGM. The battery is in a trunk and is what was suggested for this car but it is still vented, so this is the reason I went with it. It's my very first experience with one so I really didn't mind trying it. The car is not a high cranking needing car supposedly, but I guess you won't know until you try it. LOL. I do agree, I have a very old wet cell on my other car and that battery is still going. I know it's really old too because I forgot how long I had it, but that car is like the energizer bunny, as long as I keep the internals clean it just keeps going and going.

It sounds like you know your stuff too - or at least suspect correctly - I'm merely confirming it. So did your car originally have a wet cell? For audio buffs etc wanting "audio" batteries, I usually suggest keeping the original wet cell main/cranker (even if perhaps upsizing it) and fitting an AGM close to the amp. After all, going to the trouble of getting an AGM for its lower internal resistance only to still have the cabling resistance to the amp... And then that AGMs do not like cranking currents etc. Plus the secondary AGM can be an emergency jump start battery. But if only one battery is possible, then I can understand using an AGM (even if it does lower peak SPL LOL). You also said your AGM was vented (or did you mean the boot/trunk?). AGMs are considered "sealed" tho yes, they have a vent. That's where their original name is clearer - VRLA = Valve Regulated Lead Acid (or Valve Recombination Lead Acid) - where the valve is the vent but it requires pressure to operate; ie it does not let the hydrogen vent, it keeps it to be recombined when charging. The valve is only to prevent pressurised case explosions due to heat or excessive gassing (eg, charging >14.4V, or less if any cell has collapsed). What I mean to say is that although your AGM is technically vented, it isn't.    [ ?? ] AGMs are great in that you can leave them 12 months without a recharge. That's by spec for a fully charged battery; some are fine after 2 years. As to my mate that started his car for the first time in THREE years with the battery still connected... That was my "real" intro to AGMs - specifically a Gates 40AH as used by telcos. I had no doubt the car would start, but I laughed at the suggestion that the battery would have any juice whatsoever. I hate people that ignore my laughs and have the last laugh. The recharge time for full wet cells is generally accepted as being 3 months. Of course both assume full charge, and no discharge (parasitic draws), and healthy batteries. (Old batteries self discharge at higher rates.) Usually "internal" batteries must be sealed by law (eg AGM), else in a sealed enclosure vented to the outside. However many OEM vehicles have internal wet cells. Even tho the same safety issues apply, the fact that they are OEM and approved means "they" can have wet cell internals, BUT it does not mean WE can add an internal wet cell. (Some people have difficulty understanding such legalities.) You may read some old threads herein about me and my 38AH Yuasa UPS AGM. Tho IMO is should never have suited my main battery & cranker application, it faired well. That Yuasa UXH series is designed for heavy discharge UPS applications and they have a 10 year design life, but that does not mean it will last long if used often (to full or near full discharge at max currents). I got mine when it was replaced after 5 years (a standard preventative maintenance/service procedure for essential systems like UPS) and did not start using it until it was 10 years old (excluding some camping/solar trips). I used it as the sole battery for about 3 years before deciding to save it for "real" applications and getting a new wetcell main battery. I decided to use it as a main after my brother said he had been using his for years. The fool! - I only gave it to him for use as an emergency battery; I never expected it to last as a cranker. (I think he's still using it. It's at least 14 years old and he's been using it for at least 5 years.)   But they were oldskool Yuasas - IMO Yuasa was always a quality battery, but whether that still applies since the Chloride(?) buy in... One of my learnings was the typical "non exercised" capacity. I used it as a secondary battery for a fridge etc before using it as the main battery. It had occasionally been charged and always seemed fine - ie, its full 12.7V etc. (Recharges were maybe every 12 months. Its OC voltage was never below ~12.5V.) It had been fully charged before fitting for the fridge. I used an MW728 battery protector - a 10A cig-socket battery protector aka low voltage cutout which disconnects at 11.2V and reconnects (I think) at 12.5V - and I noted it was clicking... What was happening... The OC battery voltage was ~12.7V. The MW728 would connect the ~4A cooler and the battery voltage dropped to 11.2V within ~15 seconds. The 728 disconnected and battery voltage quickly returned and after the 728's turn-on delay - a requirement for all such circuits including "smart" etc battery isolators - of ~15 secs the cooler was reconnected and the cycle would repeat. That is ridiculous for a healthy battery of that size. But as I suspected, it needed a good high-current run. Sure enough, a short 5-10 minute drive fixed the problem once and for all. The lesson - sometimes chargers cannot give the same current that an alternator can provide. (It was an 8A charger which IMO should be fine...) It also confirmed what we experienced people know - battery voltage does not indicate actual capacity, it merely indicates its %age of capacity - ie, 12.7V is full capacity even if that is a mere 5AH and not its new/rated 38AH. Incidentally, tho I never formally capacity tested that AGM, a few years later I had to limp home with headlights and no alternator. It was a 1 hour country trip and a quick head calculation (based on an assumed 15A loading - no hi beams!) suggested it should last 2 hours if it was still healthy (ie, 80% or more of its initial or rated capacity). I got home without trouble. In fact after ~15 minutes my dash voltmeter confirmed my assumed loading (or rather, predicted battery voltage) was pretty good and I'd get home easily PROVIDED the battery didn't suddenly die. (A battery, especially old, may seem to discharge fine and then suddenly collapse without warning.) The next day my DMM confirmed it was about 50% discharged which meant it was as good as new despite its 13 year age (3 years beyond its "design" life & 8 years after it was scrapped for UPS reliability reasons). Ok, that was a lot of ramble, but FWIW. You don't have an Optima. IMO that's good. IMO they were once good batteries but they took a dive a decade or 2 ago. Some still swear by them, but I know of too many failures. My battery supply Guru stopped stocking Optimas ages ago - and disappointingly Odyssey which I held in high non-practical regard - due to high return rates etc. He recommends Deka which I read are well regarded stateside as well. Also IMO Kinetik get god reviews stateside. FYI - I found out my UXH38-12 retailed for AUD$670 but the UXH100 (or UXH110?) retailed for $500. So 2.5 times the capacity and 25% cheaper. And if the 38AH handled my starter, a 100AH would romp it in. (My starter was 240A until I changed to a 140A reduction starter.) With ~70AH Optimas retailing for $450 (maybe $350 in practice) I had no doubt which battery I'd choose - ie, the Yuasa UXH100-12. I'd be surprised if that did not last at least 20 years. However since then a Guru-recommended dual-terminal ~110AH wetcell for $220 so that'll be my eventual camper & remote choice. (Main battery, maybe a 2nd in the engine bay AND/else another under the vehicle.) Apparently they are great as crankers for 4WDs, and for winching, and as deep cycle solars. That is unusual in that batteries are either crankers (high current) else deep cycles (low & slow current) by physical design, or a compromise between the two. Maybe it's a deep cycle but being so big (as for big AGMs) high currents are not such a big deal. Geez I ramble!

LOL...no problem I don't mind. Yes I believe the one I took out of the car was an original AGM, so this is why I also went with one. The battery does have vent tubes on it, so they get vented to the outside. For now I just let this car sit and drive my other car to see if it goes down. So far it keeps turning on when I move it. I just move it to save me the parking space. I have also heard about the quality on those optima's going down. Then again I don't think I can even buy one, they are pretty expensive. I really don't mind using the wet cell if it works in the trunk with the vents, but if there's a problem with those in a trunk even with a vent, then I don't know. I also have never tried one there yet, so I can't say whether it works or not. Of course the consensus is better to use an AGM there. I don't know. The good thing about having the battery back there is how easy it is to make my amp connections. They are about two or a little more for the power if any. So very nice and clean. The down side is that the car is pretty small, so not much room overall. Your story reminded me when I was younger and I left a girlfriends house around midnight...then my car at the time would not start...I had to push start the damn thing by myself...oh the dumb trips you make when your young...LOL