Router battery

I have a contract with Vodacom which includes a Huawei router. Recently the router battery swelled up and was on the verge of exploding. I went to Vodacom to buy a new battery but they don't sell them only the router with a battery included. Eventually I had to buy a new router with battery when the old router was fine. This seems very unfair as the new router costs around R900 whereas a battery would be much less. This has also happened to a friend who has the same router. Vodacom should do something about this and not just rely on selling new routers.