Car battery: Regular lead acid vs AGM?

[JEDI]

my car has an always cigarette lighter plug.

sometimes i forget to unplug and drains the battery.
when that happens, the battery will never recharge to full.
Do this a few times and the battery has trouble starting the car in the winter.

I read AGM batteries are good for always on cigarette lighters:

https://www.costco.com/automotive-batteries.html

So AGM batteries are deep discharge?
It recharges back to full even if you completely drain the battery?

 

[mindless1]

Not all AGM batteries are deep cycle. The deep cycle type would be what you want for the deep drain lighter powered widget but not for high current in cold winter starting. If your lighter powered widget keeps draining with no termination from low voltage, even a deep cycle AGM will have substantial lifespan decrease from doing this a few times, if it drains down near 0%, and I'm not entirely sure if it applies to agm too but I know flooded can freeze and break open at higher and higher temperatures (still below freezing) the lower the state of charge.

Why not just rewire the lighter outlet to only come on with vehicle aux or ignition on? If you can't find a circuit with current to spare, use a circuit that's only live with aux or ignition, to trigger a relay in series with the existing circuit for the lighter, as any circuit will be able to spare a few tens of mA to trigger a relay.

Amazon has 30A automotive relays for around $5 & up, just needs to be a typical normally open relay, or you could get a two pack of whatever type is used on your vehicle and have one to spare if ever needed.

Example: https://www.amazon.com/Standard-Motor-Products-RY601-Relay/dp/B000C7ZVN2

 

[BonzaiDuck]

Not all AGM batteries are deep cycle. The deep cycle type would be what you want for the deep drain lighter powered widget but not for high current in cold winter starting. If your lighter powered widget keeps draining with no termination from low voltage, even a deep cycle AGM will have substantial lifespan decrease from doing this a few times, if it drains down near 0%, and I'm not entirely sure if it applies to agm too but I know flooded can freeze and break open at higher and higher temperatures (still below freezing) the lower the state of charge.

Why not just rewire the lighter outlet to only come on with vehicle aux or ignition on? If you can't find a circuit with current to spare, use a circuit that's only live with aux or ignition, to trigger a relay in series with the existing circuit for the lighter, as any circuit will be able to spare a few tens of mA to trigger a relay.

Amazon has 30A automotive relays for around $5 & up, just needs to be a typical normally open relay, or you could get a two pack of whatever type is used on your vehicle and have one to spare if ever needed.

Example: https://www.amazon.com/Standard-Motor-Products-RY601-Relay/dp/B000C7ZVN2

i can understand that vehicle cigar lighters are wired in the way the OP describes, but I wouldn't know why -- can't even guess why. On my Ride, the lighter is powered through the ACC or Accessory fusebox lead. One must turn the key just to the notch before ignition, and it is powered. I think the radio and the side-mirror robotic motors are powered off the same fusible link from the battery. I would investigate key settings and circuits closed in the factory manual, and see what amperage spec (@ 12V ? ) supplies the accessory or similar switch-setting. There should -- or might be some unused capacity.

I would also suggest getting a trickle-charging device to keep your battery charged up. Just remember to disconnect it properly and close the hood before you back out of the garage. For me, I just remove the positive and negative leads in the car, put on the copper clamps from charger and connect everything, plug in the charger and come back periodically to watch it during a day every month or so.

I prefer AGM batteries now to the traditional lead-acid constructions. They seem more resilient. With a few full discharges, they will still last through their warranty period and maybe beyond it. What? Maybe 5 years? If you want a deep-cycle, people may have various preferences and arguments, but I use the Optima Yellow Top. Of course, my Trooper is an SUV, a conventional SUV is built like a truck, and so the battery I use probably fits a pickup truck.

If you need to give 12V power to various devices, you can avoid using the cigar-lighter port, and get a portable Lithium-Ion rechargeable generator, like a Westinghouse iGen600s. Carry it around in the car when you know you need to power something. Charge it up at home.

 

[Raizinman]

Don't do it. AGM Batteries charge at a lower rate. If you put one in a vehicle that had a regular battery you will overcharge the AGM and ruin it in short time. The charging systems, charge at different rates.

 

[BonzaiDuck]

Don't do it. AGM Batteries charge at a lower rate. If you put one in a vehicle that had a regular battery you will overcharge the AGM and ruin it in short time. The charging systems, charge at different rates.

It hasn't happened to me. On my 95 Trooper, I ran a red-top Optima for five years, then replaced it with a yellow-top. I've had no alternator problems and no battery problems. I had no problem with the red-top over that five years, but the battery had been totally discharged out of negligence about three times, and that's supposed to shorten longevity.

The solid-gold mechanic's advice to everyone is straightforward. Do you check the air in your tires and top up every couple months? Then -- charge up your battery with a charger once every couple months. Most people settle into a type of complacency, and leave the little troubles for the mechanic when they get their annual checkup and oil change. But it's a minor chore.

 

[Raizinman]

It hasn't happened to me. On my 95 Trooper, I ran a red-top Optima for five years, then replaced it with a yellow-top. I've had no alternator problems and no battery problems. I had no problem with the red-top over that five years, but the battery had been totally discharged out of negligence about three times, and that's supposed to shorten longevity.

The solid-gold mechanic's advice to everyone is straightforward. Do you check the air in your tires and top up every couple months? Then -- charge up your battery with a charger once every couple months. Most people settle into a type of complacency, and leave the little troubles for the mechanic when they get their annual checkup and oil change. But it's a minor chore.

Have you noticed that when you purchase a battery charger, there is normally a specific setting for AGM? This is because the charge rate is different.

 

[Meghan54]

Don't do it. AGM Batteries charge at a lower rate. If you put one in a vehicle that had a regular battery you will overcharge the AGM and ruin it in short time. The charging systems, charge at different rates.

Damn...so I put an AGM into my '03 Chevy Silverado about two years ago. So how long does it take before the battery go tits up?

 

[Torn Mind]

Build quality matters more than technology. Optima is the best known AGM brand but the negative anecdotes after Johnson Controls got it and moved manufacturing to Mexico means that lifespan may not be better than flooded. AGM is great for odd orientations and lower likelihood of attacking the terminals by leaking.

 

[BonzaiDuck]

Build quality matters more than technology. Optima is the best known AGM brand but the negative anecdotes after Johnson Controls got it and moved manufacturing to Mexico means that lifespan may not be better than flooded. AGM is great for odd orientations and lower likelihood of attacking the terminals by leaking.

See -- I'll stick with that assessment. Raizinman may offer some useful facts, but my empirical experience thus far -- having had three full discharges on a red-top Optima which lasted five years, doesn't seem to give something to worry about. As you say, the battery remains clean with no corrosion. We also put a yellow-top in my brother's 95 hardbody Nissan truck. We had more trouble with a conventional battery holding its charge on the truck, but vehicles need to be driven with some degree of frequency. So I put the charger on that battery as well, maybe once a month.