Power Tool Battery to Laptop PSU Converter - Page 1
Forum section: electronics / beginners

author: AFriendlyFish
author_rank: Newbie
timestamp: September 02, 2025, 10:05:02 am
content: Hi, I was really excited to discover products like (https://www.amazon.com/Regulator-Compatible-Included-Adjustable-Charging/dp/B0FC284HGK) and (https://www.newegg.com/p/2S7-09PC-00622?item=9SIC030KJT1218) which promise to let me power my laptop with safe 20V power from power tool batteries. Unfortunately, the products look super sus. Thus, I'm looking into doing a DIY project to convert the power tool battery output which seems to range from 13 V to 22 V to a clean 20 V output suitable for my 230 Watt laptop. Honestly, I'd be happy to get even 150 watts (7.5 amps) as hopefully i can power my laptop enough with that. How can I DIY this?Two alternative methods I could do are use a 140 W (28V) USB C power bank and convert it to 20V or DC to AC inverter battery and then connect my normal laptop AC adapter into the AC battery. However both of these seem unnecessarily wasteful. Is this true? Or are these legitimate approaches to consider? It seems like using a power tool battery would be way more efficient, but it seems impossible to convert this into a laptop safe power supply.Thank you!PS: I don't trust myself to play with batteries and electricity safely, so if there is an existing product that does this, I prefer buying it over DIY. So far the best I found is this one (https://www.amazon.com/Krisdonia-64000mAh-Portable-Smartphone-Projector/dp/B08V1HQ6HQ) which claims it can output 6 amps at 20V, but even then, it gives no specs about its power quality.

author: NE666
author_rank: Frequent Contributor
timestamp: September 02, 2025, 10:39:20 am
content: Quote from: AFriendlyFish on September 02, 2025, 10:05:02 amThe first product you linked seems about as well reviewed as the average Amazon product, and appears to do what you require of it. Personally, I see nothing 'super sus' about it, and in any case, if you purchase through Amazon you have *some* buyer protection. Without wishing to appear rude, based on what you've told us of your electronics skills, it's likely going to be better than something you put together yourself.Bear in mind, depending on the laptop you have and how you're using it, you might chew through batteries quite quickly and ones of decent capacity aren't cheap.I wouldn't worry about power quality, that's overthinking - your laptop's internal regulators are more than capable of dealing with some noise from a cheap switch mode power supply.

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: September 02, 2025, 03:47:09 pm
content: If you want plug-and-play safety, get a Milwaukee/Makita/DeWalt official power supply accessory (around 100–120 W output).

author: amyk
author_rank: Super Contributor
timestamp: September 03, 2025, 12:37:41 am
content: Note that "20V" for a laptop is a nominal rating, limited by 25V capacitors on the input circuitry and largely based on being able to charge a 4S lion pack (16.8V full, around 12V empty) with some headroom. They'll likely start charging anywhere from ~17V up to even 24V, although I wouldn't push the margins that thin, and if you don't actually need to charge the battery, then anything from 12V up may be enough to take the load and stop the battery from discharging.In other words, if you haven't figured it out already, an 18V power tool battery (5S, 21V full, ~15V empty) may be connected directly to a "20V" laptop's DC input, with a fuse or additional protection if desired.

author: Eurora
author_rank: Contributor
timestamp: September 03, 2025, 02:56:15 am
content: Using a power tool battery as a laptop power source is definitely possible, you just need a clean and safe way to regulate the voltage. The simplest DIY approach is to use a high-quality DC-DC buck-boost converter that can take the variable battery voltage (typically 13–22 V depending on charge state) and hold a steady 20 V output. Choose one rated for at least 200 W so it won’t run at its limits, and set the output voltage precisely with a multimeter before plugging into the laptop. For safety, it’s a good idea to add an inline fuse near the battery to protect against short circuits, and pay attention to correct polarity. If your laptop uses USB-C PD, you can pair the converter with a PD trigger board so the laptop negotiates 20 V properly. This direct DC-DC method will be much more efficient than going through a DC-AC inverter or charging a separate power bank first, and as long as you check voltage and polarity carefully before connecting, it’s a very practical solution.

author: amyk
author_rank: Super Contributor
timestamp: September 04, 2025, 02:13:18 am
content: There's no need to do another round of DC-DC conversion. The B+ of the laptop is already stepped down to the various other voltages needed.

author: AFriendlyFish
author_rank: Newbie
timestamp: September 05, 2025, 05:13:45 pm
content: what is the "B+" of the laptop?

author: Andy Chee
author_rank: Super Contributor
timestamp: September 06, 2025, 04:07:17 am
content: The terminology "B+" is a hang over from vacuum tube and CRT electronics, where it referred to the highest DC voltage rail on the board (vacuum tubes this would be the anode/plate supply, whilst in the case of the CRT it would be the flyback supply voltage, rather than anode).In the context of this this thread, B+ is whatever voltage your laptop takes as input, which very very likely will be the highest DC voltage in the laptop circuitry (of course, excluding the rectified mains, which is not in the laptop but inside the powerbrick).

author: amyk
author_rank: Super Contributor
timestamp: September 07, 2025, 02:23:11 am
content: I meant B+ as in the battery voltage rail, which does get pulled up to DCIN when plugged into an AC adapter, but is otherwise the rail that sources all the other, lower voltage ones.

author: AFriendlyFish
author_rank: Newbie
timestamp: September 17, 2025, 01:51:24 am
content: I'm thinking of using this product (with a 25.6V battery [to buck voltage]):https://product.tdk.com/en/search/power/switching-power/dc-dc-converter/info?part_no=RGA24250W014A-003but the data sheet (https://product.tdk.com/system/files/dam/doc/product/power/switching-power/dc-dc-converter/catalog/rga_e.pdf) says my load cannot have a capacitance of more than 2200 uF. Do most laptops have an effective capacitance less than that? Also, I'm worried if I have a CPU withdrawing random amounts of current at 3.5 GHz, then perhaps that rapid change in current demand will be too rapid for my DC converter to keep up with??