101Leafy researched the games.
Full Voltage

A Thunder Sac gives this a Thunder element. The tradeoff is size. Shelling Lv2
| Class | Gunlance |
|---|---|
| Rarity | 7 |
| Attack | 460 |
| Thunder | 180 |
| Slots | 1 |
| Price | 50,000z |
Upgrades
| Upgraded from | Hard Bone Lance+ |
|---|---|
| Upgrades into | Full Generator |
Can also be made new at the smithy.
Upgrade tree from モンスターハンターポータブル 2nd G 公式ガイドブック (Enterbrain, 2008), page 760.
Materials
Khezu Hide - Tan ×8, Thunder Sac ×5, Carbalite Ore ×10, Rubbery Hide+ ×5