Profoto Acute LiFePO4 custom battery

26650 4.5Ah 14V LiFePO4 yay, I made a battery

I had a previous post detailing my research on an alternative power source to the Profoto branded battery for the Acute B.

After exhausting my search for a battery within spec for the job and in some form of personal protest I made a battery. Not so much made as assembled a battery of batteries with some protective circuits but still, it’s a project!

WARNING: Lithium batteries can explode or catch on fire, they can dump massive amounts of power, will melt things and burn up your devices. Build and use at your discretion, this is a record of what I have done not a suggestion that you do it.


26650 4.5Ah 14V LiFePO4 battery build

First off, my design spec… it had to fit in the original battery cassette, handle at least 26A draw and I didn’t want to exceed 14V which pointed to LiFePO4 cells over LiPo which would have given 16… and done who knows what to the electronics. I wanted it to cost less than $650, and preferably not take hundreds of hours to build. It’s a battery, not a car. It took about $100 and probably too many hours but if I want to make another…. maybe two hours not including print time.

In the first photo you can see the cassette, with the original Pb gell cell removed. You can 3d print the cassette for the 26650 cells from this design.

25560 cells can be bought in several chemistries. LiFePo4 gave me comparable voltage to the original PB. I had wanted to use a different cell made by Nitecor originally but thought 3.7V cells combined to make 16V might increase the chance of catastrophic failure. I used Tenergy 26650 cells. You can buy A123 cells, same capacity for double the price. The reviews were favorable on Tenergy, I have used their NiMh cells in previous projects, I’ll tell you next year how the 26650’s hold up.

26650 4.5Ah 14V LiFePO4 battery build

BMS Board- Battery balance and protection PCB. This allows you to charge the battery using a relatively stupid LiPo charger and to not blow things up. It took a while to source a board that could supply up to 30A continuous and fit in the box. This just made it, barely! It can peak discharge over 100A, kind of scary but there’s a fuse on the cassette as well to limit it to 40A. Note, the board didn’t work at first. After removing it, I found a reference online that mentioned hooking it to a charger to reset it. Bit of a pain that I had desoldered it but after successful testing with a batch of alligator clamps I put it back together and went on to live testing. How to wire it or “the secret spec sheet!”





Just because I can… I had previously printed a custom jumper set that allowed me to power up the Acute B with the battery outside the generator that was able to handle serious amperage. I was concerned that battery clamps might short out on the bench. It’s overkill but that’s what you do when you have a 3d printer. It has lights to indicate correct polarity and a power meter to catch peak draw. I metered the original Pb cell at 24A, a drop in replacement LiFePo4 I bought five years ago which is no longer available at 25A, then my new homebuilt cell at 31A. Pretty nifty, likely I’ll get a bit faster recycle on the unit. I might consider that as the cassette has a 40A fuse on it and hopefully the pack has it’s own internal temperature monitoring I’ll be safe… but then the heads for this system are not fan cooled so I’ll have to be aware to not overheat the heads/pack. It’s rare that I’m rapid firing at full power for any length of time, and for that matter on huge shoots I usually rent equipment.

battery normally goes inside the rig powerpack, power meter/test rig in use

Note: the . I have it wired externally to test it… I’ll have to upload the files for the rig perhaps…

Thanks to Jamie Allegre for initially putting the test rig on an oscilloscope to get power readings and see charge profile. The initial tests kept me from buying a bunch of possible replacement that would have just shut down on start up. Thanks for Michael Curry for encouraging me to fry my pack… enough to make me second guess the LiPo pack I bought and never test it on the rig.

Profoto Acute B Lithium Battery Upgrade LiFePO4

I have a 1st generation Profoto Acute B, 600ws pack/generator. The original battery is a Lead Acid I’m documenting my second and current attempt to find a suitable LiFePO4 (Li) 3rd party replacement.

update…. I built a battery… check out the new post…

My beloved AcuteB so this post isn’t all words

 I have a 1st generation Profoto Acute B, 600ws pack/generator. The original battery is a Lead Acid (Pb) 4.5Ah 12V in the form factor of a home alarm backup battery. Several times I have re-celled the batteries and attempted to use 3rd party cells with mixed results detailed below in addition to a current attempt to find a suitable LiFePO4 (Li) 3rd party replacement. 

Profoto sells replacement PB cells for about $65 and a replacement LiFePO4 battery for $655. You can find 3rd party Pb cells for as little as $20 and LiFePO4 for $60 but don’t expect them to work so easily.

My first attempt at using an off the shelf Pb 4.5Ah (PowerSonic PS-1250) in 2010 was lousy, where the original would give about 160 full power flashes, it gave about 45 and never rose the battery level out of the red zone.  

A few months later I purchased a Tenergy 4.5Ah LiFePO4 which is no longer on the market and was getting over 200 full power flashes per charge. I should have bought four of them.

Recently as the performance of the Pb and Li cells have sharply dropped, I began shopping for another drop in Li and it’s turned into an engineering project. After a two month wait for the only drop in I could find out there, a CTC LiFePO4 I was disappointed that the cell would shut down when the generator was powered up. I’ll go into the details a bit more below and document my attempts to avoid dropping $655 which just seems like a steep hike… until you start doing research.

The Profoto AcuteB is rated at 600J output per flash and charges the capacitor bank in under 2 seconds using a stock PB 12V 4.5AH 

with a 40A automotive fuse on the battery case. Speaking with a tech on the phone at Silvino’s in LA I found the approximate surge pull on the battery was 30A. He was also searching for a feasible LiFePO4 solution.

Considering the lack of a drop in replacement I began looking at configured and tested packs that might fit into a 3d printed battery case vs building a pack using off the shelf cells and protection circuits.

So far, I’m unable to find a preconfigured pack that will supply over 22A peak discharge let alone the 30-40A I need. In conversation with a battery tech, we surmised that it would be possible to wire a large capacitor in parallel to the battery pack to buffer the peak draw, keeping it from shutting down during the initial surge and also lengthening the life of the batteries as a bonus.

Breaking out a calculator and the internet, I did a little math to see how this would work.

The AcuteB has a rating of 600WS or 600J
WS = Watt Seconds
J = Joules
S = Second
A = Amps

I’d like to cut the peak draw from 30A down to 20A, if a capacitor could hold 14.5V 10A it would appear that I might be able to make this work. A few more google searches and scribbles and I calculated I need a 15V 1F cap or (5)2.5V 5F caps in series parallel with the battery to do the job. Here’s where I need someone to chime in and tell me it won’t fry.

Q=Coulomb=1A/1S 1Amp supplied for one Sec
C=Capacitance (Farad F) 1F cap can store 1Q
C=Q/V for Parallel
1/Ceq=1/C1+1/C2… series

Alternative Solution: I spoke with a tech today at bioenno power about a 4.5Ah pack with 18A peak cutoff and a 6Ah with 24A peak cutoff . The tech said that they could be programmed to cut out at a higher current though it would decrease the battery life/charge cycles though pose no danger of overheating.

AcuteB battery $250, replacement cell $65, carrier $190? for what?