[BimmerNugget]

I plan on doing OFHG soon and some coolant needs to be drained, thus air will enter the cooling system when I'm done and a bleed procedure will be needed.

When bleeding the system, many people say to plug in a battery charger to prevent the battery from draining. Is this necessary? My battery is fresh, only 1 year old and I recently took my car on a little road trip (300 miles), so the battery should be fully charged by the alternator.

The bleed procedure takes 12 minutes, will the water pump really drain a fresh battery in just 12 minutes of usage??

I'm really trying to save that $40 and not buy a battery tender if I don't have to.

[Bimmer Pleaser]

Just get another car, run it and parallel the batteries. That's how I bled my cooling system.

[Biginboca]

Originally Posted by Bimmer Pleaser

Just get another car, run it and parallel the batteries. That's how I bled my cooling system.

This.

[Welcome to NBA Jam]

I'd highly recommend a battery charger.

[e90yyc]

You’ll be fine without one.

I ran the bleed procedure multiple times on my quite-new battery and no issues at all.

[BimmerNugget]

Originally Posted by Welcome to NBA Jam

I'd highly recommend a battery charger.

Ehh, I'd rather not spend $40 on something that's only going to be used 1-2 times. All my cars are daily driven, it's not like I have a Ferrari 488 garage queen that needs to stay charged when it's not driven for extended periods. Also, I'm not one to buy a tool, use it, then return it. If it's not 100% necessary for this process, then I won't get it. Thank you for your responses.

[arkie6]

A trickle charger wouldn't do anything for you here. A typical trickle charger puts out around 1 Amp. Assuming you had it on the battery for the entire 12 minutes during the bleed procedure, that is 1 Amp x 12/60 Hr = 0.2 Amp-Hr. That is 0.2% of the capacity of a typical 90 Amp-Hr 335i battery. Even a full capacity 10 Amp charger isn't going to do much in 12 minutes: 2 Amp-Hr or ~2% battery capacity. I don't know what the current draw for the electric water pump is, but I can't imagine it is more than 20 Amps at its highest speed which translates to ~4 Amp-hour or ~4% of battery capacity.

[IllSic_Design]

I'd recommend it, but I did bleed someone's system without having a charger available and didn't have an issue. At least do as said above and run in parallel with another battery so you have no worries IMO.

[Phyrexia]

I've had a charger for 10 years and I've used it more than enough times to make it worth the purchase.

I'm sure you CAN do the bleed procedure just fine without one. But it sucks if the battery dies in the middle of any processes like that.

[e90yyc]

Guys guys guys.

I’m all for best practices, but it’s not like he’s flashing his DME where there’s literally zero margin for a dead battery.

If OP had a charger, great. But the original question was “should I buy one for this?” The answer is no. It’s overkill.

Our cars have big batteries and are able to support moderate current draws on battery alone without issue.

For example, the ‘rest’ function activates both a coolant pump and the blower motor, and will run for over ten minutes.

Absolutely nothing is going to happen if the car dies midway through, which it won’t if battery is in good shape. There’s nothing magical or uninterruptible about this process. It simply runs the water pump without the engine, that’s it.

[PichaDis11]

Originally Posted by e90yyc

Guys guys guys.

I'm all for best practices, but it's not like he's flashing his DME where there's literally zero margin for a dead battery.

If OP had a charger, great. But the original question was "should I buy one for this?" The answer is no. It's overkill.

Our cars have big batteries and are able to support moderate current draws on battery alone without issue.

For example, the 'rest' function activates both a coolant pump and the blower motor, and will run for over ten minutes.

Absolutely nothing is going to happen if the car dies midway through, which it won't if battery is in good shape. There's nothing magical or uninterruptible about this process. It simply runs the water pump without the engine, that's it.

This.

Should the car's Power Management System detects excessive power loss on the battery it will interrupt the process by turning off the ignition. This doesn't mean the battery is dead though. (Preventable if light switch is set to parking lights).

[mweisdorfer]

Originally Posted by BimmerNugget

I plan on doing OFHG soon and some coolant needs to be drained, thus air will enter the cooling system when I'm done and a bleed procedure will be needed.

When bleeding the system, many people say to plug in a battery charger to prevent the battery from draining. Is this necessary? My battery is fresh, only 1 year old and I recently took my car on a little road trip (300 miles), so the battery should be fully charged by the alternator.

The bleed procedure takes 12 minutes, will the water pump really drain a fresh battery in just 12 minutes of usage??

I'm really trying to save that $40 and not buy a battery tender if I don't have to.

No, but it's a smart idea

[mecheng77]

I give my batteries a full charge 1-2 per year on my smart battery charger, it seems to help maintain their life and puts less strain on my alternator so they do come in handy.

[Pladi]

I was actually able to do 2 full cycles of bleeding with no extra charger.. My battery at the time was original too so i think your fine.

[AoS810]

I bled mine 4 times in a row (didn't start the car to allow battery to recharge) after I did the OFHG and coolant flush. No issues at all and my car started right up. I'm on a fresh battery though, fully charged and less than a month old. That's also with the heater at max temp and fan speed at minimum, all lights off.

[TemjinX2]

if you daily drive your car...battery should be strong to go through the bleeding process long as its a healthy battery.

worst case...you would have to take out and get it charged for free at autozone or o reily's.

obviously have your rear seats down in case battery dies and you cant open your trunk.

[BimmerNugget]

Thanks your all your responses!