If you need more flight time, more battery capacity helps (to some extent) 🙂
But most batteries are designed for very high current, wires and connectors are also choosen for this purpose.
It’s sometimes a problem. I use in my tricopter standard XT60 connectors as it’s amperage is good enought for this purpose. When I used 1800-2200mAh batteries it was ok, as there come also with XT60.

When I bought 4000mAh with HXT4mm connector, I also bought adapter from HXT to XT60 for it. Problem solved.

Soon 4000mAh was not enought for me 🙂
So, I bought 5000mAh, but this battery comes with 5.5mm bullet connectors. This time I decided to change connector to XT60 instead of messing with heavy adapters.
On Polish R/C forum there is a thread about such changes and most difficult thing for people is to solder XT60 to much thicker wires. My new 5Ah battery have 10AWG wire, so it’s quite thick. There are some ways for soldering these wires and I also have one.

Because ‘seeing is believing’ or ‘a picture is worth a thousand words’, I recorded how I solder such thick wire to XT60 🙂

What you need to make it:

• tin ends of wire (mine were already tined as I desoldered old connectors instead of cutting it off)
• turn pins in XT60 in opposite direction (you could use flat pilers to do it)
• use ‘third hand’ – it’s very handy and also heat resistant
• solder one wire at a time – it’s for your safety – don’t get a chance for short circuit
• put tin into connector
• put soldering iron into tin in connector and put wire there – this way area of heating is increased, so it’s easier and faster to do it
• don’t hold wire in bare hands – use pilers, beacuse of heat
• little patience depending on power of your soldering iron (mine have 65W) and experience

Good luck 🙂