A lot of negative nellies again...
To the OP:
It doesn't take much of a battery to ignite an ejection charge. But, there's lots of tradeoffs to be made.
First, you need to decide what kind of igniter or e-match you're going to use. There are a number of threads on here about DIY igniters, there are a lot of commercial choices from rocketry vendors, there are a lot of commercial choices from fireworks vendors. Some of the choices require a lot of current (4 to 5 A at 6+ Volts), some don't require nearly as much (1A at 2V). Once you've chosen an igniter, you can look into batteries.
LiPo batteries are excellent for rocketry, because they're small, light, and can source a lot of current. From your perspective, the problem might be that you have to buy them, and a charger for them. You may be able to find them cheaply in the Radio Control hobby - for example, I've purchased these:
https://www.amazon.com/gp/product/B07MW2L96L and been quite happy with them; they provide plenty of power for my Eggtimer Quark computer and igniters. You may be able to find a similar product in your country, or on Alibaba. I would strongly recommend putting in a fully charged battery for each flight.
LiIon batteries will work fine also. They tend to be bigger and heavier for a similar level of power output, and share the same disadvantage that you may need to purchase them and a charger for them. One big advantage is that they tend to be more reliable long-term than LiPo - read the comments above about "puffy".
An Alkaline Duracell 9V battery is heavier and larger than either the LiPo or LiIon solutions. It has one big advantage - you can probably buy them anywhere. It has sufficient power to light just about any igniter out there, but I would use a brand-new one for every flight to make sure that your igniter lights. As a result, you might find that it starts to get more expensive than LiPo if you have a number of flights.
Good luck.
