Why do online UPS's have more batteries than line interactive UPS's when they are the same capacity?

I have 2 UPS's. One is an online 2KVA UPS, the other is a line interactive 2KVA UPS. The online has 6x 12V 34W batteries and the line interactive has 2x 12V 7AH batteries. They obviously support the time capacity but due to the different technologies, they support different loads and provide different... show more I have 2 UPS's. One is an online 2KVA UPS, the other is a line interactive 2KVA UPS. The online has 6x 12V 34W batteries and the line interactive has 2x 12V 7AH batteries. They obviously support the time capacity but due to the different technologies, they support different loads and provide different protection standards.

The batteries in the online UPS do not hold their charge anymore and the line interactive has not been used for more than a month so the batteries are still good. Theoretically the batteries can work in either UPS but is there a specific reason the online has six batteries and the other only two?

I opened a faulty 3KVA online UPS and it also has six batteries but each one is 12V 45W.

So I'm curious as to why there are more batteries in the one than the other when they are both from the same generation, same manufacturer and both have the same capacity?

Please, no spammers or people with pointless answers.
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