996Outpost.com

I've started to research this issue a few times as it seems to raise it's head from time to time. The situation is that your car is in storage in a place where you do not have access to plugging in a battery tender, and a solar powered tender doesn't work either (for example - your car is inside, nowhere near a window). I see people post questions on this issue regularly.

It has always been my assumption that plug-in battery tenders draw almost no power - a miniscule amount. If that is the case, it seems to me that these new lithium jump starters would store more than enough power to keep a car battery topped up for at least a month (and probably several months). Theoretically, you could attach something like a jump starter to your battery and leave it there to act as a battery tender while your car is in storage, right? Once a month you pull it off, plug it into the wall to recharge and then re-attach it to the car battery. But, after searching several times, I have yet to come across anything on the market like that. There are the plug-in chargers and the solar powered chargers, but nothing that uses a battery as the power source.

I have a couple of high-capacity lithium jump starters, and I know you can plug a USB cord into it to charge your cell phone. If the jump starter had a 110 v plug built into it, I suppose you could just attach your normal battery tender to the car battery and then plug the tender into the jump starter. But it would seem to me that there is a market for an actual battery-powered battery tender. So why are there none on the market and what am I missing here?

This is probably on some manufacturer's radar, as battery tech is improving at a geometric rate what with all of the electric car nonsense...I mean investment.

I have a NOCO GB70, a pretty hefty lithium car-starter thing that came with cables to hook up phones, etc. I experimented by hooking up my small Midland 15W GMRS radio via the proper attachment to the NOCO and left it on a weather channel to see how long the NOCO charge would last. It was dang near 24 hours, and I had to stop the test because I didn't want to go to zero charge while I was out. Now the radio was not transmitting, it was receive-only, so I'd have to calculate the actual consumption....which is math....which is not going to happen.

I think the issue with a car battery charger / manager is that even though the drain is minimal and slow, even the best deep cycle batteries would last maybe...maybe 5 to 7 days, because it would also have to power an AC converter to run the charger from a 12v battery. Most people leave a car stored for much longer. Might be worth an experiment.

I have a converter that converts 12v DC to AC and while it would not be enough to power a refrigerator, I could see how long the trusty NOCO would last with my CTEK charger on the 911.

I'll put it on the projects list.

"Battery -> inverter -> tender -> battery" would be a terrible idea. Not only are inverters terribly inefficient (the cheaper it is, the more loss there usually is), but then the tender has to transform the AC back to DC to supply the battery and that is another lossy process. If your tender is providing 1-2 amps to the battery and you were using another car battery to do it I'd bet on 30-40 hours tops.

Find yourself a Dc to DC step up/boost converter that is good for 5A at 14V and then run it through a charge controller. As long as your target battery is healthy and topped up you should be able to get 60 or so hours out of a car battery as your source.

If you do use a car battery as your source, use a deep cycle model so there is less risk of damage if it gets drained.

As far as lithium based batteries go, I would not leave them in use unattended for long periods like that. Bad things can happen if they short or get drained too low.

A charge controller similar to what the smaller portable solar set ups use? The other idea was convoluted, but then again it was motivated by Frunk's inquiry. At least I got my NOCO GB-70 charged back up after a long winter sitting in the back of the ML350. Even after months of cold, it was still about 98% charged. Those things are great.

Unrelated, but I want to look into a portable solar panel / converter / power unit for use with a mobile HAM radio setup. Many many YouTube videos on this. The only challenge is to find something that is not 100% chinese. Hard to do with electronics!!

So, Mr. Frunkenstein, the answer to your query is the standard "you can't get there from here"

The lithium jump packs also typically have a manual reset that needs to be tripped after x time and/or after each start attempt. If you don’t read the instructions on those things, you WILL go mad.

Go to batteryhookup.com and build your own fire hazard.

Obliquely related: I ruined a batch of aluminum brass by switching the proportions of aluminum and copper...and I didn’t have enough copper to fix it...so I hucked a couple of 18650 cells into the crucible. It was VERY flamey. Pro tip: do this never. But when you do, do it outside like I do.

5chn3ll wrote: ↑Sat Mar 27, 2021 11:28 am
Go to batteryhookup.com and build your own fire hazard.

This is kind of what I was thinking of creating:


It's a combination of the concepts that Einsteiger and gnat described. Personally, I like it.

Hook all those dude in series and you got something. Not necessarily something good but something!

FRUNKenstein wrote: ↑Mon Mar 29, 2021 10:41 am This is kind of what I was thinking of creating:


Battery-Mess-600x450.jpg


It's a combination of the concepts that Einsteiger and gnat described. Personally, I like it.