What is this battery pack inserted here at bottom?

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I have this adaptor powering a 5V equipment.

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I need a portable battery. What is the most reliable one that can produce 4A, 20W? I can't take chances for it to fail because the equipment is very expensive.

  • How long does the equipment need to operate for? Will it be running on this battery constantly, or just as backup? Does the power need to run through the adapter, or do you just need the 5V, 4A supply?
    – IronEagle
    Oct 8, 2019 at 4:33
  • Just need 5V, 4A supply without using the adaptor. It will be used at times only or intermittently.. not continuously.
    – Jtl
    Oct 8, 2019 at 4:37

2 Answers 2


Why try and "home-brew" something? 5V out is about as standard as it's possible to get, nowadays. Get a Lithium-Ion power-bank, something like this 26000mAh unit.

It has 4.8A max output current, and 26000mAh will do 4A for 6.5h (if that really is the capacity, these things tend to be exaggerated somewhat.)

You'd need to make a custom charger cable, paralleling the 5V & 0V lines between the ports, so as not to overrate the USB connectors, but as you're talking about making your own, I'm sure that won't be a problem.

  • Please see edited main post about added photo. What is that battery pack inserted at bottom?
    – Jtl
    Oct 8, 2019 at 7:45
  • 1
    I haven't a clue - probably something very similar, just custom-designed for this system. It's worth noting - what are the actual requirements for this device? Does is need 4A? It may be that this is just what they supplied because it's cheap.
    – SiHa
    Oct 8, 2019 at 9:59
  • @Jtl, In general, a battery pack for a tool or device is going to be 100% proprietary and won't fit anything else. Internally, most of them use 18650 Lithium cells in some arrangement with electronics for charging and discharge rate limiting. Just get a power bank and make a USB adapter cable if needed. Or buy a battery solution from the maker of the tool you have.
    – JPhi1618
    Oct 8, 2019 at 14:04

EDIT: Due to numerous changes to the original post, this answer no longer really applies. Keeping for its comments' sakes.

You'll probably want to start with a 12V battery, and use a 12V to 5V "buck" converter to supply your 5V. One that can handle 5A should be 10-15 USD, but you might want to go with a higher rating if this 4A load is constant, to give some room for error. Then figure out how long you want your equipment to run for - if you want a 10 hour backup, you need 4 * 5 * 10 = 200 Wh of capacity. For a 12V battery, if you only use the top 40% of it's capacity (for long life), you'll need a 40 amp-hour battery, ([200 / 12] * 2.5 = 41) which should run you maybe 60-70 USD. Also, when you wire all this up, make sure your connection to your equipment is the same polarity as the charger - the symbol on it says it's center-positive.

12V batteries come in a few types - AGM, SLA, Marine, car battery... I've had good luck with SLA, or Sealed Lead-Acid, myself: they are well-contained, last for 5-7 years of daily use if properly sized, and charging is simple. If your equipment is mobile, you could try some kind of Lithium rechargeable battery, you'll get good energy density, but you'll have to deal with the risk of exploding batteries, complicated charging, and a shorter lifespan.

Don't use a car battery - it will likely die after only 10 or so full charging cycles.

Lead-acid batteries have two parts to their "capacity": total amp-hours, and discharge, or "C" rate. Multiply the C-rate by the amp-hour capacity of the battery to get the amp draw that that rating applies for. For, say, a rating of 40Ah @ 0.1C, the battery will supply 40 amp-hours if you draw 4 amps continuously. The general rule of thumb is that the more current you pull out of the battery, the less amp-hours it holds. batteryuniversity.com has some excellent in-depth explanations of all this.

  • Well. I'm using it on a very expensive $15,000 molecular scanner or spectrometer. I can't take chances with assembling the battery pack with many components. So i need to buy a readily available super reliable 5V battery source. There are no brands that offer this directly, without having to experiment building one?
    – Jtl
    Oct 8, 2019 at 5:16
  • 1
    Well, if you're protecting a $15,000 piece of equipment, then I would look into a UPS. Specifically, a line interactive or double conversion UPS (uninterruptible power source). Several companies make these, and will have warranties, etc. These would just go between the wall outlet and your current adapter.
    – IronEagle
    Oct 8, 2019 at 5:59
  • I already use the most advanced surge protection device to protect it. May I know why the I need the UPS? As for the battery, I need to make it portable so I can take it outside and hold in the hand with equipment (the battery needs to be small and good for 30 mins or so only).
    – Jtl
    Oct 8, 2019 at 6:06
  • Or pls take a look at this.. biotools.us/assets/Ram532NANO_AppNotes_v5.pdf I have the R532 unit (the black one). They have a handheld unit with the battery (called Ramtest). So I just want the battery. They won't sell the battery pack to me separately because I got the R532 unit only. What battery do you think they are using?
    – Jtl
    Oct 8, 2019 at 6:09
  • 3
    @Jtl for powering a $15,000 piece of equipment, I'd figure out a way to buy the battery from the manufacturer, or talk to a competent electrical engineer about having him/her design a battery/charging system for you. It would be a shame to cobble something together based on the random advice of some well-meaning online strangers and have it blow up your equipment because you weren't able to supply every necessary detail and they didn't think to ask for them...
    – FreeMan
    Oct 8, 2019 at 16:00

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