Extensive battery usage with IVPN would not be particularly unusual for a combination of reasons, more specifically:

  1. IVPN apps offer VPN protocols with the highest level of encryption available, thus using more CPU power, which results in a higher battery consumption as a result.
  2. Mobile devices usually 'sleep' and shut down persistent network connections in favour of reduced bandwidth and energy, a solution called 'push'. However, a VPN tunnel requires constant connectivity to ensure security, and this does not utilise this power saving method.

If security is not your primary concern, to preserve the battery power consider disconnecting from the VPN connection when not in use or when your device is sleeping.

Alternatively, you may try the newly released WireGuard protocol, which was proven to provide higher performance while at the same time cause less stress to the battery.