After examining it more closely, looks like my initial suspicions of three spade connectors were dead on. It’s the grey connector that makes them easy to connect into the UPS. It can be done manually, however I would recommend an additional layer of shrinkwrap over the crimp ends (the red parts of the spades) so you can use a pair of needlenose to connect them one at a time as safe as possible.

Electrophile – I’m not sure why APC has chosen the two 12V packs in parallel but it seems to carry over with all of their multi-battery installations. Every UPS I have seen that has more than one cell is wired in a 24v configuration.

The yellow wire and resistor go to the GND cable, not the positive cable, which is a bit out of the ordinary. I would think that if they were doing some kind of amperage testing for battery runtime that they would be using the positive lead off of the 24 v arrangement than the GND.

Zorg – You might be right, the resistor might not be a current sensing resistor for loads but rather a safety lockout. If the resistor is there, wrong value or connected to V+ it might throw an alarm and not enable the battery pack at all.

As always, thank you all for your kind comments and the information in your experiences!

FIRESTORM_v1

My BR24BP factory-installed batteries are different than yours – mine have a maximum initial charging current of only 1.7A. They have the same *capacity* (size), but they are not rated for quite as high of a charging current. The UPS’s charging circuit must be designed to limit the charging current to a value that will not exceed the rating of the batteries. Since my factory BR24BP batteries can only handle 1.7A max, I would be able to use any 12V replacement battery that will fit in the BR24BP case and that is rated for a maximum initial [charging] current of 1.7A or greater (2.1A and 3.4A are other values that I’ve seen).

and chris, i create myself too a “compatible” plug with separate pin. the most important is avoid bad connection and short circuit between pin (crash fuse )

[sorry for errors, i'm not english]

Thanks for a great hack!
These pictures are really worth a thousand words. This article is especially for people who want to know what is inside a BR24BP because they either don’t have access to or do not own one…

As an Electronics Engineer, I have 3 confusions:

1. Paralleling battery packs is not recommended because it can lead to circulating currents both while charging and discharging process. This scheme though works would adversely affect life of the batteries. APC battery pack does not seem to follow is rule at least according to the picture!! Wouldn’t it be better to use 2 batteries each of rating 12 Volts 18 Ampere hour in series?

2. I cannot understand why yellow wire in the internal battery pack is connected to positive and the one on the external battery pack is connected to negative even if it is through some resistor.

3. The way yellow wire is wired to negative terminal (before the fuse), current sensing can happen only if the voltage is sensed across the fuse. In this picture, yellow wire with the negative line (going toward the UPS) are connected together with just a resistor in between. I checked the voltage on the male terminal (back of BACK-UPS RS1000) and found it to be about 2.1 volts, and possibly means this resistor is creating some kind of voltage divider so that internal electronics can sense if there is an external battery pack connected? Maybe to alter the total charging time?

Would appreciate if someone can enlighten me!!

One thing is sure, with this article of your and a little common sense of electrical connections, one can surely make a decent and low cost external battery pack instead of buying an expensive BR24BP which technically (IMHO) will not have a reliable operating life.

Thank you both for your comments. I haven’t heard back from the engineer friend about the resistor although it does appear that the correct value is 20Kohm as initially suspected.

I’m extremely tied up at the moment between Mardi Gras and Valentine’s Day but will update the article as soon as I have a few moments to disassemble the pack again. I would rather take the time to do a thorough investigation instead of going off of a hunch so look for another update around tuesday the 16th.

Thank you all for your kind words, I’m thrilled that the information posted here is helping out so many people.

FIRESTORM_v1

Could you give a picture,in which order those 3 wires are crimped to the jack? If I don’t get a similar jack, I will try to get 3 separate jacks so would like to know the order.

Derek and Shaaz….have you tried this yet

it’s true, resistor at 4 (the most popular and not ambigous lecture code?), 5, and 6 colors are simple, but… not always lol

after research on factory resistor for discern, clearly, difference between notation 4, 5, 6 ring color, i’m find this:

http://www.vishay.com/docs/49478/ms0002.pdf

http://www.vishay.com/docs/20143/colorcod.pdf

if that can help us