Question for electrophiles...

[Johnologue]

Most portable power banks aren't made for pass through charging.

Yeah, realized and looked that up partway through writing. "Most" isn't "all", but the limitation is enough to make it seem a lot less plausible.

 

[phidauex]

At least one of the recent review videos had a picture of the frunk with the 12V battery access door on the left side open. Anyone remember which video? From that we should be able to estimate the size of the battery. It looked reasonably large, something like a group H3 battery, 30-40 Ah rating? Sometimes possible to cram a slightly larger battery into the same space by sliding the brackets out or using lower profile terminals. (The MachE has an H3, but I've heard some people have slipped an H5, slightly longer, into the same space).

I don't think anyone needs to worry about standby drain from "normal" automotive 12V accessories that use an always-on source, but are designed well and go into a deep standby at 1-10 mA of load.

For a 30 Ah small EV battery, 10 mA would consume 10% of the 12V SOC in 300 hours. Not really a concern. I know that some of the android units and car-puter units have much higher standby consumption, but they can also usually be set to go into full standby after a delay, like 30-60 minutes.

I think most users will not need to do any big dance with additional batteries and DC/DCs unless they are trying to power something huge (giant stereo, winch) or something always-on at far higher than normal load (always on car-puter).

My MachE is riddled with always-on telematics so that the cell modem can wake up the car, and it recently sat idle for 2 weeks, and dropped 3% of 12V SOC, on a 35 Ah battery. That would be less than 1 mA of standby load (or the DC/DC turned on at some point during that time and it doesn't show up in my data).

I do recommend a little monitor like these (https://www.amazon.com/dp/B01MT4583U). I have one on both of my vehicles, it has a miniscule load of its own, and it lets you quickly sync and check the 12V voltage and SOC.

 

[tubes]

Here ya go. Start time loaded for you.

 

[phidauex]

Here ya go. Start time loaded for you.

Nice, that is a great shot of it. From the pixels, and making some assumptions, it really looks like an H3 or a Group 35 AGM battery, meaning 30-40Ah. If my measurements are off or that isn't the final battery, then it is at least something in that size range.

 

[r6tn]

I think your conclusion might be right but your measurements might be off. The only group 35s I see are around 9 inches wide (228mm), depending on the brand. But I think the top post would be 0.625 or around 15.8mm. That should make your measurement on the width closer to 9in.

 

[phidauex]

I think your conclusion might be right but your measurements might be off. The only group 35s I see are around 9 inches wide (228mm), depending on the brand. But I think the top post would be 0.625 or around 15.8mm. That should make your measurement on the width closer to 9in.

Good point, I think I had the wrong terminal top dimension. Tricky when they are tapered, and positive and negative are different dimensions. If the left post is negative (seems most common for H3 batteries), then the top is 15.9mm.

That gets me to a width of 174.3mm, which is very close to the 175mm width of an H3 AGM battery. So I'll revise my prediction to H3 AGM, 35AH, rather than a Group 35.

 

[Trace26]

Good point, I think I had the wrong terminal top dimension. Tricky when they are tapered, and positive and negative are different dimensions. If the left post is negative (seems most common for H3 batteries), then the top is 15.9mm.

That gets me to a width of 174.3mm, which is very close to the 175mm width of an H3 AGM battery. So I'll revise my prediction to H3 AGM, 35AH, rather than a Group 35.

okay, so how do I wedge a bigger one in there...

 

[r6tn]

Good point, I think I had the wrong terminal top dimension. Tricky when they are tapered, and positive and negative are different dimensions. If the left post is negative (seems most common for H3 batteries), then the top is 15.9mm.

That gets me to a width of 174.3mm, which is very close to the 175mm width of an H3 AGM battery. So I'll revise my prediction to H3 AGM, 35AH, rather than a Group 35.

Stupid me, I thought that would make the width measurement wider for some reason. It's been a long day I guess.

I looked up some stuff and am going to confuse things. Sorry in advance!

Group 35 batteries use SAE terminals with the negative side being 15.9mm
H3 batteries use DIN Type A1 terminal with the negative side being 17.9mm

Your initial 18mm might have been right but it would still be close to an H3.

Aside from that, the top of that battery sure does look like an H3 with the T shaped raised part (circled). And for what it's worth, you're right about positive being on the right. The positive side has the terminal with bolts sticking up for a Hall sensor or whatever, plus this looks like the negative cable hanging there (arrows).

 

[SL8action]

If the intent is to run a 500W+ sound system, a secondary battery may make sense. That does not seem to be the case here. Is the primary concern the stereo will drain the 12V battery to the point that the EV will not start up? I suspect that is unlikely to happen, but to alleviate the concern, a low voltage protector in line with the stereo might be all that is needed. Set it to cut out at about 50% charge level (12.1V):
https://www.amazon.com/dp/B07YTVK1JK
https://www.amazon.com/dp/B0F2LWHKTY

 

[Daemoch]

Ive run some decently sized sound systems (1200w-4800w) in my daily drivers and never needed a second battery, but that was ICEV with HO, modded, or 3rd party alternators. I installed Caps to account for voltage drops in a couple, but that was it. Ive never needed to use a second battery but Ive seen it done plenty of times, usually more for visual impact than for any good reason.

It might be prudent to look into motorhomes and campers for some established solutions?

Anything under a few hundred watts I dont think i'd be too worried about it unless youre trying to run it for extended periods, and in that case I think you might want a standalone audio power source, or to look at building out from the main Slate pack, not the stock 12v it has already. I'd assume the 12v its got has a capacity/load matched inverter tying it to the main pack system. Without changing that, Id be worried about over drawing it.

Until we get some solid detailed and granular specs and real diagrams though, its all just speculation on our side.

 

[Cubicle23]

Most portable power banks aren't made for pass through charging.

Get the ones made for solar input like the Voltaic. They are designed to charge and discharge simultaneously due to the variable nature of the sun strength. Essentially they take what they can when they can to try and keep it topped off. I was a serious bicycle tourist for decades and used a system like this for years, taking a small solar panel and the rectified output from a front generator hub to keep a Voltaic battery charged as a buffer , phone ran nearly 100% of the time I was riding.

Here is vid on the bicycle charging system if anyone is curious.